3 dimensions of a cubic box and 2 dimensions is square area. Cubic measurements you are multiplying 3 dimensions. In this particular case the measurements are given, hence: 3×3×2.
The question gives height, width but not length. It gives depth units as 2 and also height 3 which is confusing because height and depth are usually the same. In this instance we shall assume the 2 units are the length.
To calculate the volume of a cuboid or prism you have to calculate the base area multiply by height.
Volume = base area (length × width) × height.
Base area = 3 × 3 = 9 units
Height 2 units
So now,
(Base area) 9 × (height) 2 = 18 units.
Hence since it is a prism. Also can be calculated;
Volume(prism) = Ar(base)×h
Volume(cuboid) = (lb)h = 3×2×3 = 18 unit²