you are looking for the smallest number that is divisible by 4, 81, and 3
look at prime factorization
4 = 2*2
81 = 3*3*3*3
3 = 3
For the least common multiple look for the maximum number of each factor. So 2 2's and 4 3's is the maximum. 2*2*3*3*3*3 = 324