I need to know how to set this problem up:

The foundation of a house is 13m by 7m. If the builder increases each dimensions by the same amount, the area will increase to 135sq m. Find the new dimension.

okay so he's increasing both dimensions by x

to start with you have 13*7

to end with you have (13+x)*(7+x) = 135

now you can multiply out, rearrange, solve for x, then work out the new dimensions.