For 14, the person bought too much sand. only 30 cubic feet of sand can fit into that sandbox(LxWxH). 6 feet by 5 feet by 1.2 feet would be 6(length) x 5(width) which is 25 and then 25(L&W) x 1.2(height) which equals 30 cubic feet. And that's your volume. You got volume by using length x width x height.
