JSFiddle - React, Tailwind, and code Playground

HTML

Average product unit value <input type="text" id="product-unit-val" /><br/>
Total unit sales value <input type="text" id="total-unit-sales" /><br/>
Number of reps <input type="text" id="number-reps" /><br/>
Total sales value <span id="sales-val"></span>$

JavaScript

$(function() {
  $('#product-unit-val, #total-unit-sales, #number-reps').keyup(function() {
   var total = parseInt($("#product-unit-val").val()) *  parseInt($("#total-unit-sales").val()) * parseInt($("#number-reps").val());
   if (!isNaN(total)) {
      $("#sales-val").html(total);
   }
  });
});