I don't quite understand your topic sentence however to my best knowledge This is what i've come up with:
Rectangle 1 and 3 are the same. The only known side is the width at 5 inches whilst the other is unknown so it will be h.
Rectangle 1 and 3 area are "5h"
Rectangle 2 has a width of 8 and a length of h. Its area is "8h"
Without triangles our TSA for the rectangles is: 2 X 5H + 8H = TSA
The triangles are both assumed to be the same are. To get the Are of one it is [tex] \frac{1}{2}*(B*H) [/tex]
Which = 12
Ans: TSA = 18H + 24