Matrix field calculation

But I would like to know if I could calculate the total figures each week?  The field is a text box.

Considering that you are using matrix field, inside of this guide you can find out how to perform form calculation in the Matrix field:

http://www.jotform.com/help/343-How-to-perform-form-calculation-in-the-Matrix-field 

Hope this will help. Let us know if you need further assistance.