If the area of the large rectangle is 147 units squared, what is the perimeter of the shaded area.

There is a visual of a large rectangle divided into four smaller ones. One is shaded. The area is given for the other three: 48 and 15 along the top half of the large rectangle and shaded area plus 28 on the bottom half.

I tried adding up the different known areas and subtracting it from 147 but 56 makes no visual sense looking at the picture. HELP!!

This problem is killing me. Thank you!