Hey You!
The formula for area is length × width. So, let's try all of them:
9 × 8 = 72
9 × 9 = 81
9 × 10 = 90
9 × 11 = 99
Judging by all the possible lengths above, the only two answers that would provide an area either equal to 90 of greater than 90 are:
X=10 and X=10