the length is 18ft
and width is 16ft
we know that the perimeter of a rectangle is equal to

which l and w stand for length and width.
so if we divide 68 by two, we will have the sum of the length and width.

so the sum of length and width is 34(68/2)
and sum of ratios is 17 (9+8)

so if we multiply the ratios by 2 we can find length and width

good luck