[Hekumok]

<table>
		<tr>
			<td id="inputA">31920</td>
			<td><input type="text" size="2" id="inputB" onkeyup="addIt()"></td>
			<td id="output"></td>
		</tr>
	</table>
<script>
function addIt() {
	var value1 = parseInt(document.getElementById("inputA").innerHTML) ;
	if(isNaN(value1))
		value1 = 5 ; //это для проверки
	var value2 = parseInt(document.getElementById("inputB").value) ;
	var sum = value1 * value2 ;
	var textout = + sum + ' р.' ;
	document.getElementById('output').innerHTML = textout ;
} ;
</script>