The least common multiple can be found by prime factorization or simpy listing the factors! You must know what the least common multiple that goes into 9 and 12.
Prime factorization of 9 and 12 is 3 so 3x2x2x3=36
Or you can list the factors
9: 9,18,24,36
12: 12,24,36
So the least common multiple is 36