Please help, 20 points.
Perimeter :)

Answer:
Step-by-step explanation:
Look at the picture.
The dimensions of the picture:
(42 - 2x)in × (32 -2x)in
The formula of an area of a rectangle:
A = l · w
l - length, w - width
Substitute l = (42 - 2x), w = (32 - 2x) and A = 900
(42 - 2x)(32 - 2x) = 900