Explanation:
Since all the alternate edges are different in length, the box is a cuboid. Surface area of cuboid is calculated by:

Given measure of length = 21 ft, width is 7 ft and height is 10.1 ft. Surface area of the box is:
= 2(21*7 + 10.1*7 + 21*10.1) ft²
= 859.6 ft²
Surface area of the block is 859.6 ft²