update array

i have this values come from form

"explainanswer": {
"53": "yes php framework ",
"54": "not javascript ",
"55": "not security",
"56": "not forensics "
},
"answer": {
"53": "php framework",
"54": "javascript",
"55": "security",
"56": "forensics"
},

i have table answers with this fields

`id`,`answer`, `explain_answer`,

how can update this fields depend on id , id come from table as above 53,54,55,56

i try this code but not work

        foreach ($request->answer as $key=>$val){
            $answer=Answer::findOrFail($key);
            $answer->answer = $request->answer[$key];
            $answer->explain_answer = $request->explainanswer[$key];
            $answer->save();
        }