function roundNumber(rnum, rlength) 
{
  var newnumber = Math.round(rnum*Math.pow(10,rlength))/Math.pow(10,rlength);
  return(newnumber);
}
 
function calculate()
{
	charges=parseFloat(document.getElementById('txtCharges').value);
	average=parseFloat(document.getElementById('txtAverage').value);
	if(charges>0){}
	else
	{
		alert("Please enter a valid 'Number of Credit Card Charges per Month'.");
		document.getElementById('txtCharges').focus();
		return(false);
	}
	if(average>0){}
	else
	{
		alert("Please enter a valid 'Average Charge' amount.");
		document.getElementById('txtAverage').focus();
		return(false);
	}
	total=charges*average;
	result1=total*.0275;
	result2=total*.0175;
	result=result1-result2;
	
	document.getElementById('resultID').innerHTML=roundNumber(result,2);
}