Llamar a variables

Good afternoon

I would like to tell you about my doubt:

I am making a budget oriented to the reforms and in the possibilities is that the user chooses the dimensions of the room.

For some options in the budget it is necessary to choose that dimensions in square meters has the room and depending on those dimensions put a price so that in the end what I mean is that as data an element can take the value of another element.

Is it possible to give the condition that the user transforms the dimensions in m2 and that according to these square meters the price can be set?

Thank you very much, best regards

The page I need help with: [log in to see the link]