6. Factor out the greatest common factor.
24a3b2 + 48ab3 - 42a4b
The biggest number that goes into all of the coefficients is 6. All of the terms have at least one factor of a and one factor of b. Factor out a 6ab.
We can tell that we have factored out the greatest common factor because there is no common factor for the terms in the parentheses.
At this point we see if there is some other way that the expression inside the parentheses can be factored in any other way, but it cannot.