The lengths of the sides of two similar rectangular billboards are in the ratio 5:4. If 250 square feet of material is needed to cover the larger bill-board,

how much material, in square feet, is needed to cover the smaller billboard?

This is my work:

5x + 4x = 250

9x = 250

I then divided and got a decimal number.

I knew then that my answer was wrong.

I played with this question for 20 minutes in vain.

Help!