Answer:
To find the surface area of a rectangular prism you must multiple the length and the width. You can choose the top and do 2(L*W) and one of the square sides 2(L*W) and the front 2(L*W) and add it all up.
2(L*W)+2(L*W)+2(L*W)= surface area
There is a 2 because there are two side of a rectangular that are the same. Since there are 6 sides on a rectangle. Only 3 pairs are similar.
Hope this helps :)