Which of these is a common multiple of both 3 and 5?

To determine a common multiple of both 3 and 5, we can begin by identifying the multiples of each number.

The multiples of 3 include: 3, 6, 9, 12, 15, 18, 21, 24, and so on.

The multiples of 5 include: 5, 10, 15, 20, 25, and so on.

A common multiple is a number that appears in both lists of multiples. By examining both sets, we can see that 15 is present in both the multiples of 3 and 5.

This makes 15 the least common multiple (LCM) of both numbers as well, since it is the smallest multiple that both 3 and 5 share. Therefore, 15 is indeed a common multiple of both 3 and 5.

The other choices do not satisfy the condition because they either belong to only one of the lists or do not appear in the multiples of both 3 and 5. Thus, 15 is the correct answer as a common multiple.