Each edge of the box is 3 ft, and to get the volume we need to do L * W * H. Because all three are 3, it's just 3 * 3 * 3, which is 27 ft³ for the volume of the box.
Now, what's the volume of 10 of these boxes? To get that, we just multiply the volume of the original box by 10. 27 * 10 makes 270 ft³.