The width of a rectangle is 9in, shorter than its length

The area of the rectangle is 252 in2

What is the length of the rectangle

I think the length is 21 in because ...

the width (W) is x-9

X (x-9) = 252

X^2 - 9x-252=0

(X-21) = 0 and (x+12) = 0

x=21 or x=-12

the only one that works is 21 and I checked the answer so I'm pretty sure it's 21

I believe the length is 28in