Starting with the expression:

First, notice that both terms have a common factor of x. Therefore, rewrite the expression as:

Next, notice that 30=15*2. Therefore, both 15 and 30 have a common factor of 15. Rewrite the expression again factoring out 15:

Since the greatest factor of 1 is 1, then the expression has no further common factors.
Therefore, the greatest common factor is 15x.

The final factored expression would be:
