CAN YOU ADD OR SUM NUMBERS

Yes. It is possible to perform calculations using JotForm by using our Calculation widget. Please refer to the guide below that can help you with calculations in your JotForm. 

http://www.jotform.com/help/259-How-to-perform-calculation-in-the-form

The guide is provided with step-by-step instructions and graphical illustrations along with a video and demo form for better understanding.

Hope this information helps.