function calculate(){
  var unit_price = ((2099)*.10+(2099));
  var input = document.getElementById('num_people');
  var num = (unit_price * Number(Math.round(input.value))).toFixed(2);
  if(isNaN(num) == false && Number(input.value) == Math.floor(input.value)){
    var output = document.getElementById('cost');
    output.value = num;
  }else{
    alert('Please enter a whole number only!');
  }
}

$(document).ready(function(){
  $("#form").validate({
    rules: {
      num_people: "required",
      company:  "required",
      address:  "required",
      phone:  "required",
      email:  "email"
    },
    messages: {
      num_people: "Please enter how many people will join ",
      company:  "Please enter your company name",
      address:  "Please enter your address",
      phone:  "Please enter a phone number",
      email:  "Please enter a valid email address"
    }
  });
});