We can see that since p2 equals 12 times an integer (q2), p2 is divisible by 12. Since 12 is divisible by 4 and 3, p2 is divisible by 4 and 3. Would this be possible if p wasn't divisible by 2? what about by 3? Remember that p will have a prime factorization (2 and 3 are prime numbers), and so will p2 (how is the prime factorization of p2 related to that of p?)