adding a new row with one cell of type math

Suite and Optimus Suite 5
#1

How can I add a new row to a grid whose last cell is (as loaded from xml schema) of type math and which shows its value based on a formula (let’s say c3*c4)?
xml portion:
Gross Value
sample xml data:

…
=(c3+c4)*c5

and finally the ‘insert-new-row code’ :

var newId = (new Date()).valueOf();
ListGrid.addRow(newId, “”, ListGrid.getRowsNum());
ListGrid.selectRow(ListGrid.getRowIndex(newId), false, false, true);

#2

Try to put math formula into the value of last cell in a row.
For example:

mygrid.addRow("newRow",",,,,,=c3*c4",ind)