Can the first three rows of the Matrix tool be added and totaled on the fourth row?

Can the first three rows of the Matrix tool be added and totaled on the fourth row?

This can be accomplished using the Spreadsheet calculation: https://widgets.jotform.com/widget/spreadsheet 

https://www.jotform.com/help/252-How-to-Add-a-Widget-to-your-Form

Let us know if you need more help.