Change image size live when form field entered

Following on from some helpful advice on this forum, I have tried to develop a solution to a problem. Basically, when a user enters their bespoke widths into two seperate form fields (#input_9_2 and #input_9_3) I want an image or div layer, or table, to change shape in relation to the entered field entry. So if say, a user enters 20cm in field one and 300cm in field two, the image/div/cell will automatically before their eyes show that shape (using cm as pixels - this 20 px wide x 300px high). This is the code I have been using but it just isnb't working - I have no doubt my argument / syntax is wrong but can anyone help - I'm now three days into this and have tried very hard to sort myself. Many thanks.

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<img class="sbimg" id="sbimg" src="/wp-content/uploads/2012/06/AAF-Splashback-Black-Gloss-Splashback-Full-No-Handle-200x200.jpg">
<script>
$(function width(){
  $('#input_9_2').keydown(function(){
    setTimeout(function() {
      $('#input_9_2').val();
    }, 50);
  });
});
$(function height(){
  $('#input_9_3').keydown(function(){
    setTimeout(function() {
     $('#input_9_3').val();
    }, 50);
  });
});
var photo = document.getElementById('sbimg');
var photoWidth = width();
var photoHeight = height();
photo.width = photoWidth;
photo.height = photoHeight;
</script>

Hi Chris - link to page here, just select 'custom sizes' to see the section I'm talking about: http://www.thesplashbackfactory.com/splashback-products/black-steel-splashback-12mm

new code:

<img class="sbimg" id="sbimg" src="/wp-content/uploads/2012/06/AAF-Splashback-Black-Gloss-Splashback-Full-No-Handle-200x200.jpg" width="200" height="200">
<script>
$(function width(){
  $('#input_9_2').keydown(function(){
    setTimeout(function() {
      $('#input_9_2').val();
    }, 50);
  });
});
$(function height(){
  $('#input_9_3').keydown(function(){
    setTimeout(function() {
     $('#input_9_3').val();
    }, 50);
  });
});
var photo = document.getElementById('sbimg');
var photoWidth = width();
var photoHeight = height();
photo.width = photoWidth;
photo.height = photoHeight;
</script>