Let L, H, W be the length, height, and width.
Using the 3 clues they gave us, we have:
L x W = 12
L x H = 8
W x H = 6
Our goal is to figure out volume: L x W x H
One way of solving this is to just randomly plug in numbers which should be easy to do for this problem.
Another way is to use substitution.
From first equation: L = 12/W
Plug that into second equation:
12/W x H = 8,
H = (8/12)W = (2/3)W
Plug that into the third equation:
W x (2/3)W = 6,
W x W = 9
W must be equal to 3.
And since we know that L x H = 8
Then L x H x W = (8) x 3 = 24 cm^3