How to Post Submission Data to Thank You Page

Hey There

I am trying to create a contact form that will post submission data to the thank you page.

Scenario:
Collect info from form and perform calculations that are displayed on thank you page.

Multiple calculations are needed:
EG:
Firm 1 = $x based on form submission data
firm 2 =$y based on same form submission data

Reason for showing calculated results on thank you page:
To capture information - otherwise users will not submit info if they can see the results on the same page prior to submitting data.

What form plugins can do this? I have tried to build this using Gravity forms- but haven't been able to create the full functionality

http://kamandizi.creativewebconsult.com/motor-insurance/

Enclosed: screenshot of ideally what results should look like after submission.

Please advise- thank you