S.O.S. Mathematics CyberBoard

I am making a Self Storage calculator for http://alquilertrastero.com.es

But when I make the selector of the furniture and household appliances I want that if you select a washing machine and a dishwasher only takes 0,8m2 because it takes one above the other in order of 1,6m2 if you select both of them.

I want that selector put one above the other automatically. Is it complicated?


Thank you!