1st problem, it would be 2,304 in. cubed. You do 24 * 8 * 12, as you are doing length * width * height to find the volume of a box.
2nd Problem, if you only get one measurement, that means that the length, width, and height are all the same measurement. Therefore you would do 4.2 * 4.2 * 4.2. If you get a decimal, round it to the nearest whole number. Therefore your answer would be 74 in. cubed.