I used javascript for my autocalculate and it works and now my problem is how can I SUM the total from autocalculate and the Data from other textbox.

here is my code:

function autocalearn(oText)
if (isNaN(oText.value)) //filter input
alert('Numbers only!');
oText.value = '';
var field, val, oForm = oText.form, TotEarn = a = 0;
for (a; a < arguments.length; ++a) //loop through text elements
field = arguments[a];
val = parseFloat(field.value); //get value
if (!isNaN(val)) //number?
TotEarn += val; //accumulate
oForm.TotEarn.value = TotEarn.toFixed(2); //out

The scenario is I have a Amount textbox and it has a value from database. And I have textboxes which is autocalculate and the total of that is display in total earn and now i want that the total earn and total amount will SUm and display in total earn..

PHP Code:
<input name"Amount" class = "LFieldTot" type="text" maxlength="12" tabindex="0" size="12" value="{$Amount}readonly="readonly"/> 
Thank you...

I tried to put {Amount} in Total Earn Values but when I insert data in the earnings textbox the data was the calculate from the textboxes, it did not sum the Amount.