The surface of the rectangle

The surface of a rectangle of sides 3 and 4 is 3 * 4 = 12. You can count that!

The surface of the rectangle with sides a and b = ab, a and b are real numbers.

The volume of the rectangular block

The contents of the rectangular block with sides 3, 4 and 5 is

3 * 4 * 5 = 60.

Count them if you like.

The volume of the rectangular block with sides a, b, c = abc where a, b and c are real numbers.