First you need to find the prime factorization of each number. You can use a factor tree to organize your factors.

Factors of

Code:

36: 2 x 2 x 3 x 3
60: 2 x 2 x 3 x 5
135: 3 x 3 x 3 x 5

* Note how the prime factors are neatly lined up.

The LCM is 2 x 2 x 3 x 3 x 3 x 5 = 540.