Let L is the length and W is the width of the rectangle. We have; L = W - 8 the area is L x W = 9
or (W - 8)W = 9 --->>> W^2 -8W = 9 --->>> W^2-8W-9=0 --->>>> (W-9)(W+1) = 0
so W=9 or W=-1 the solution W=-1 is rejected since we can not have a negative width.
So W=9 and L=9-8=1 so area is 9*1=9 sq units