Need to save 3 records using one eloquent relationship

I want to save this API output to 03 tables. Employee , Salaries,Designations how could i do it using single code line ?

{
    "emp_no": 1,
    "birth_date": "1981-11-26",
    "first_name": "Abba",
    "last_name": "Subba",
    "gender": "m",
    "hire_date": "2020-02-15",
    "salaries": {
        "salary": 90000,
        "from_date": "2020-01-02",
        "to_date": "2020-02-01"
    },
    "designations": {
        "title": "Consultant",
        "from_date": "2020-01-02",
        "to_date": "2020-02-01"
    }
}

Employee.php

<?php

class Employee extends Model
{

    public function salaries(){
        return $this->hasMany(Salary::class,'emp_no','emp_no');
    }

    public function designations(){
        return $this->hasMany(Designation::class,'emp_no','emp_no');
    }
}

Salary.php

class Salary extends Model
{
    use HasFactory;

    public function employee(){
            return $this->belongsTo(Employee::class,'emp_no');
    }


}

Designation.php

class Designation extends Model
{
   .........
    public function employee()
    {
        return $this->belongsTo(Designation::class,'emp_no');
    }
.........

}

EmployeeController.php

 public function store(EmployeeRequest $request)
    {

           $data = $request->validated();

        $emp = Employee::create($data);
        $emp->load('salaries')->save($data['salaries']);

        $designations = $data['designations'];
        $emp->load('designations')->save($data['salaries']);

     
    }