HEL DUE TODAY. The product of the sum of twelve and a number x and the difference a number x and two

$7.50x+$4.50y=midk it's been awhile since i've done one of these

Use pythagorean’s theorem and find the missing side lengths of the two smaller triangles and add them together
13^2 - 12^2 = 5
15^2 - 12^2 = 9
5+9 = 14
14 is the length of each side of the square
14^2 + 14^2 = 19.8
19.8 is the diagonal length of the inside if the square