When dealing with 3-Dimensional objects such as a box, the depth of that object refers to the distance between the highest and lowest points of that object. Therefore since it the question it states that the length, width and depth is 24 inches. Then the height of the box (as well as maximum height) would be a total of 24 inches. This would be in the case that the entire box was cubed, if the box is triangular with a square base then this height would be shorter as all the points would meet in a shorter position.
