The dimensions are those of a cuboid. A rectangle only has 2 dimensions, length and breadth. A cuboid has 3 dimensions and 6 surfaces and it has volume. The area of top and bottom=10*7.5=75. The longest sides each have area=10*5=50 and the remaining sides 5*7.5=37.5 each. When we add all 6 together we get surface area=2*75+2*50+2*37.5=150+100+75=325. If we take the top and bottom to be the largest sides, then we could say that the perimeter has a lateral measurement of 2*10+2*7.5=35.