Explanation:
First, we must take into account that there will be 3 pairs of sides that are the same. Starting at the front, we have 9 * 12. Since the rectangular prism is measured in units squared, this side is 108 units squared. The opposite side is the same. Our current total is 216 units. The side is 15 * 9. This is 135 units, multiplied by 2 since it has the other side, to get 270 units. Our current total is 486 units, so it already can't be A. The top and bottom sides are 15 * 12 units, giving us 180 on each, 360 in total. 360 plus 486 = 846 units squared.