Function is undefined

JavaScript
3

ok, well heres what I did. I placed the at the end of the page

<!DOCTYPE HTML>
<html>
  <head>
    <meta charset="utf-8">
        <title>Assignment #4</title>
    <link rel="stylesheet" type="text/css" href="css/style.css">
 </head>
 <body>
  <span>
    <img id="dynamic-image1" src="images/zero.gif" onclick="flipImage1()"> umber (1-5)">
  </span><span>
    <img id="dynamic-image2" src="images/zero.gif" alt="">
    <input type="text"  id="number_two" placeholder="Please Enter a Number (1-5)">
 </span>
<script>
...
</script>
</body>
</html>

I thought that was the way to set it up