Question: what is the least common multiple of a prime number?
Answer: The prime factors of 4 are 2 and 2, the prime factors of 6 are 2 and 3. So the least common multiple will be the maximum number of factors of 2 (that's two) and the maximum number of factors of 3 (that's one). So it is 2 x 2 x 3 = 12. For a harder example, consider 84 and 315.