Find the least common multiple of 21 and 6.

**Solution:**

The multiples of 6 are 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, ...
The multiples of 21 are 21, 42, 63, ....
We see that the smallest number, which is found in both series is 42. Therefore it is the LCM of 21 and 6.