Untitled

<!doctype html>
<html>
  <head>
    <title>Gas price calculator</title>
        <meta charset="utf-8" />
        <script>
           function calculate(){
              document.getElementById("answer").innerHTML=
                    document.getElementById("litres").value*1.382+" euros is the price you have to pay for this amount of 95 octane gas.";
           }
        </script>
  </head>
  <body>
     <h1>Gas price calculator</h1>
         <h4>(Octane number 95  - price as of 10th September)</h4>
         <div>
           How many litres you want to buy:
           <input type="text" id="litres" />
           <input type="button" value="Enter" onclick="calculate()" />
         </div>
         <div id="answer">

         </div>
  </body>
</html>