A Different Type of Mat
10. Francesca decides that, instead of gluing her photo on top of a mat, she will buy a mat that goes over her photograph and then place the photo and mat in a frame.
This type of mat has a rectangular hole in the center. The hole is exactly the size of the photograph.
Find the polynomial expression for the area of this mat. Explain your method.
(4 points: 3 points for finding the expression and 1 point for the explanation of the method)