javascript - 使用JS计算值并将该值存储在数据库中

我正在用js计算2值：

$('input').keyup(function(){ // run anytime the value changes
    var firstValue  = Number($('#user_send_fund_amount').val());
    var secondValue = Number($('#fixed_amount').val());
    document.getElementById('user_receive_fund_amount').value = firstValue * secondValue ;
document.getElementById('user_receive_fund_amount').setAttribute('readOnly', true);
document.getElementById('user_receive_fund_amount').removeAttribute('readOnly');`

并尝试存储此值：

<form  method="POST" class="form-register" action="{{ route('order.store') }}">
 @csrf
   <input id="user_send_fund_amount" type="number" class="form-control"
     name="user_send_fund_amount" required>
    <input type="number" value="{{$receive->buy}}" class="form-control"
        id="fixed_amount" hidden>
    <input type="number" class="form-control" id="user_receive_fund_amount" name="user_receive_fund_amount"/>
</form>

我的问题是：如何将计算出的值存储在DB中？