A boy has nine trousers and 12 shirts. In how many different ways can he select a trouser and a shirt?

A. 21
B. 12
C. 9
D. 108

Explanation:

The boy can select one trouser in nine ways.

The boy can select one shirt in 12 ways.
The number of ways in which he can select one trouser and one shirt is 9 * 12 = 108 ways.