I think all you gotta do if use the measurements given to you! The 15 large boxes and 7 medium boxes are unnecessary information that will not help us figure out how much volume the storage unit has. So with that out of the way, all you've gotta do it multiple 8 * 9 * 5 (and you can multiply it in any order, it's the same result)!
8ft * 5ft = 40ft
40ft * 9ft = 360ft
So the volume = 360ft cubed. Please tell me if I missed anything! I hope I helped! :)
