1 it might be worth making the question Array (Multi Flexi) (Text) (attribute: numbers only) into it's own question type
2 add the following attributes:
Show totals
* row = total for each row (an additional column)
* col = total for each column (an additional row)
* both = totals for both columns and rows (an additional row and column)
store totals in results
* 1 = store column/row totals in results
Grand total
* 1 = show grand total only
* 2 = store grand total in results (do not display)
* 3 = show grand total and store in results
Java script would calculate totals for columns/rows and would be able to hand negative numbers and floating point numbers.
for visual example see
