showing result of calculating in textbox with jquery

Question

I want to calculate division of 2 TextBoxes's value (that shouldn't be empty) and show result in another new TextBox. How can i do that with jquery?

These are my code that don't work:

 $(document).ready(function () { 

    var payNumber=  $('#InsPayNumber').val();
    var insurancePrice=  $('#InsurerInsPrice').val();


    if (payNumber!=null && insurancePrice!=null) {

        if (  $('#HasInsPayWitTax').checked) {

            $("#InsPayInstallmentPrice").val( ( insurancePrice*3/100)/payNumber);
        }
        $("#InsPayInstallmentPrice").val( insurancePrice/payNumber);

    }else {
        $("#InsPayInstallmentPrice").val("");
    } 

});

Thanks.