What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
You can use our Calculation Widget for that purpose. Here's how: http://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field.
If you need to total all field value selection, you can also do it using our calculation widget. I see that you have Radio Button fields that is configured to have a pricing. You can then pass it to the Payment Field with a donation option.
Let us know if you need any further assistance.