Форуми / Cotonti / Extensions / calculator plugin

i'm looking for a very simple calculator plugin that shows on the index.
it is to calculate the volume of a room, like length x height x width, and multiply that times a factor and just show the outcome

i got this for the TPL file, but since i have no php knowledge i don't know how to turn this into a working plugin...

can someone help me with this?

<!-- BEGIN: PLUGIN_CALCULATOR -->

<form action="" method="post">

<input type="text" name="l" value="F" /> x <input type="text" name="h" value="H" /> x <input type="text" name="w" value="W" /><br /><br />
x
<br /><br />
Factor <select namme="factor"> <option value="30">30</option>
<option value="40">40</option>
<option value="50">50</option>
  </select> = OUTCOME HERE

<input type="submit" name="submit" value="Go" />

</form>

<!-- END: PLUGIN_CALCULATOR -->

Added 21 hours later:

or is this very hard to do? i am willing to pay/donate a small amount for it :)