Bill Total - A better approach ?

There should be a better way to do this (Refer to the mount method)

       foreach ($bill->billItems as $billItem) {
           $this->billTotal += $billItem->qty * $billItem->rate;
       }

       foreach ($bill->billAccounts as $billAccount) {
           $this->billTotal += $billAccount->amount;
       }

The entire livewire class looks like this

<?php

namespace App\Http\Livewire;

use Carbon\Carbon;
use App\Models\Bill;
use App\Models\Comp;
use App\Models\Item;
use App\Models\Account;
use App\Models\Company;
use Livewire\Component;
use App\Models\BillItem;
use App\Models\Category;
use App\Models\BillAccount;
use Illuminate\Http\Request;
use Livewire\WithFileUploads;

class BillForm extends Component
{
    use WithFileUploads;

    public Bill $bill;
    public BillItem $billItem;
    public BillAccount $billAccount;

    public $users;
    public $companies;
    public $comps;

    public $categories;
    public $items;
    public $accounts;

    public $billItems;
    public $billAccounts;

    public $billTotal;
    public $billItemAmount;


    public $confirmingBillItemDeletion = false;
    public $confirmingBillAccountDeletion = false;

    public $selectedCompany = null;
    //public $selectedUser = null;
    public $selectedComp = 1;
    public $selectedCategory = null;
    public $selectedItem = null;
    public $selectedAccount = null;

    protected function rules()
    {
        return [
            'bill.company_id' => 'required',
            'bill.comp_id' => 'required',
            'bill.reference' => 'nullable',
            'bill.description' => 'nullable',
            'bill.date' => 'nullable',
            'billItem.bill_id' => 'nullable',
            'billItem.item_id' => 'nullable',
            'billItem.job_id' => 'nullable',
            'billItem.account_id' => 'nullable',
            'billItem.description' => 'nullable',
            'billItem.qty' => 'nullable',
            'billItem.rate' => 'nullable',
            'billItemAmount' => 'nullable',
            'billAccount.account_id' => 'nullable',
            'billAccount.description' => 'nullable',
            'billAccount.amount' => 'nullable',
        ];
    }

    //Customize validation
    protected $validationAttributes = [
        'selectedCompany' => 'provider',
        'selectedCategory' => 'category',
        'selectedItem' => 'item',
    ];

    public function updated($propertyName)
    {
        $this->validateOnly($propertyName);

    }


    public function updatedSelectedCategory()
    {
        $category_id = $this->selectedCategory;
        $category = Category::findOrFail($category_id);
        $this->items = $category->items;
        $this->selectedItem = $category->items->first()->id;
    }

    public function updatedBillItemQty()
    {
        $this->billItem->rate = $this->billItemAmount / $this->billItem->qty;

    }

    public function updatedBillItemRate()
    {
        $this->billItemAmount = $this->billItem->qty * $this->billItem->rate;
    }

    public function updatedBillItemAmount()
    {
        $this->billItem->rate = $this->billItemAmount / $this->billItem->qty;
    }

    // Delete BillItem Show Modal
    public function confirmBillItemDeletion($id)
    {
        $this->confirmingBillItemDeletion = $id;
    }

   // Delete BillItem
   public function deleteBillItem(BillItem $billItem)
   {
       $billItem->delete();
       $this->confirmingBillItemDeletion = false;
       return redirect(request()->header('Referer')); //To refresh the page
   }

    // Delete BillItem Show Modal
    public function confirmBillAccountDeletion($id)
    {
        $this->confirmingBillAccountDeletion = $id;
    }

   // Delete BillAccount
   public function deleteBillAccount(BillAccount $billAccount)
   {
       $billAccount->delete();
       $this->confirmingBillAccountDeletion = false;
       return redirect(request()->header('Referer')); //To refresh the page
   }


   public function mount(Bill $bill, BillItem $billItem, BillAccount $billAccount)
   {
        $this->bill = $bill ?? new Bill();
        $this->billItem = $billItem ?? new BillItem();
        $this->billAccount = $billAccount ?? new BillAccount();

        $this->bill->date = Carbon::now()->format('Y-m-d');
        $this->bill->comp_id = 1;
        $this->companies = Company::all()->sortBy('name');
        $this->comps = Comp::all();
        $this->categories = Category::all();
        $this->items = Item::all();
        $this->accounts = Account::all();

       if($bill->billItems->count() > 0 )
       {
           $this->billItems = $bill->billItems; //To display existing billItems
       }

       if($bill->billAccounts->count() > 0 )
       {
           $this->billAccounts = $bill->billAccounts;
       }

       foreach ($bill->billItems as $billItem) {
           $this->billTotal += $billItem->qty * $billItem->rate;
       }

       foreach ($bill->billAccounts as $billAccount) {
           $this->billTotal += $billAccount->amount;
       }

   }

    public function save($action)
    {
        //$this->validate();

        // Bill is in create mode
        if($this->bill->id == null)
        {
            $this->validate([
                'bill.company_id' => 'required',
                'bill.comp_id' => 'required',
                'bill.reference' => 'nullable',
                'bill.date' => 'nullable',
                'bill.description' => 'nullable',
            ]);


            Bill::create([
                'company_id' => $this->bill->company_id,
                'comp_id' => $this->bill->comp_id,
                'date' => $this->bill->date,
                'reference' => $this->bill->reference,
                'description' => $this->bill->description,
                'entered_by' => null,
                'verified_by' => null,
                'paid_by' => null,
            ]);

            $lastBillId = Bill::latest()->first()->id;

            return redirect()->route('employees.pays.bills.edit', $lastBillId);
        }
        // Bill is in edit mode
        else
        {
            if($action == "addBillItem")
            {

                //Bill::latest()->first()->id;
                $this->billItem->fill([
                    'bill_id' => $this->bill->id,
                    'item_id' => $this->selectedItem,
                    'job_id' => $this->billItem->job_id,
                    'account_id' => $this->billItem->account_id,
                    'description' => $this->billItem->description,
                    'qty' => $this->billItem->qty,
                    'rate' => $this->billItem->rate,
                    'paid' => null,
                    'verified' => null,
                ]);

                $this->billItem->save();
            }

            elseif($action == "addBillAccount")
            {
                $this->billAccount->fill([
                    'bill_id' => $this->bill->id,
                    'account_id' => $this->billAccount->account_id,
                    'description' => $this->billAccount->description,
                    'paid' => 1,
                    'verify' => 1,
                    'amount' => $this->billAccount->amount,
                ]);

                $this->billAccount->save();
            }

            elseif($action == "addBill")
            {

                $this->bill->fill([
                    'company_id' => $this->bill->company_id,
                    'comp_id' => $this->bill->comp_id,
                    'date' => $this->bill->date,
                    'reference' => $this->bill->reference,
                    'description' => $this->bill->description,
                    'entered_by' => null,
                    'verified_by' => null,
                    'paid_by' => null,
                ]);

                $this->bill->save();
            }
            return redirect()->route('employees.pays.bills.edit', $this->bill->id);
        }


    }

    public function render()
    {
        return view('livewire.bill-form');
    }
}

My Preference is to insert each and every record (BillItem and BillAccount) to the database (E.g. - 20 BillItems required 20 Submits per Bill)

However, i prefer to calculate $this->billTotal in a much optimized way

class Bill extends Model
{
..
..

    public function billItems()
    {
        return $this->hasMany(BillItem::class);
    }

    public function billAccounts()
    {
        return $this->hasMany(BillAccount::class);
    }


}