We perform prime factorization on both numbers.
Prime factors are prime numbers. These numbers can only be divided by 1 and itself.
42 ÷ 2 = 21
21 ÷ 3 = 7
2, 3, and 7 are prime factors: 2 * 3 * 7 = 42
63 ÷ 7 = 9
9 ÷ 3 = 3
3 * 3 * 7 = 63 OR 3² * 7 = 63