First, you need to multiply each of these numbers. This is a rectangle so you would do l*w, l*h, and h*w. You would do all of these things and then multiply each expression by 2 to complete the equation. Then add all of them together and you have your answer. The reason you multiply by two is because there are 2 versions of this for each equation. The top and bottom, the two vertical sides, and the two horizontal sides. 7.5*4.5*2=67.5, 7.5*3.25*2=48.75, and 4.5*3.25=29.25. Now add. 67.5+48.75+29.25=145.5 as our grand total.
The answer is 145.5in^2