$(document).ready(function(){
  var loanAmountBox = $( "[name=loanAmountBox]" );
  var interestRateBox = $( "[name=interestRateBox]" );
  var loanPeriodBox = $( "[name=loanPeriodBox]" );
  var calculateButton = $( "[name=calculateButton]" );
  var monthlyInterestBox = $( "[name=monthlyInterestBox]" );
  var totalInterestBox = $( "[name=totalInterestBox]" );
  calculateButton.click( function() {
    var carLoanInfo = calculateCarLoanInfo( loanAmountBox.val(), interestRateBox.val(), loanPeriodBox.val() );
    monthlyInterestBox.val( carLoanInfo.monthlyInstalment );
    totalInterestBox.val( carLoanInfo.totalInterest );
  });
});