Calculations in Powerpoint

We want to produce a salesman’s Powerpoint show where the user can ask questions as they go along, and fill in a form shown onscreen.
At the end of the presentation we want to have a summary which does calculations eg how many widgets do you want? = 30. 30 widgets @ 10p each will cost ?3.00.

We don’t want to edit an Excel screen with the client in full view.

Can this be done with tables, perhaps?

Thanks in advance.