Answer:
$12
Step-by-step explanation:
42 - 6 = 36
36/3
12
Step-by-step explanation:

Factor by grouping,

Complete the square, with the x variables,

Factor out 25 for the y variables

Complete the square

Simplify the perfect square trinomial

Make the right side be 1 so divide everything by 25.

Here our center is (7,2).
The answer to this problem would be 12. If you need to show work just comment.
Perimeter of rectangle:2(length+width):2(13+7)=40
Perimeter of square:4(length of one side):4(x)=40
X=10