Factor the expression

20g3 + 24g2 - 15g - 18

First, put parenthesis around the first two numbers and the last two numbers.

(20g³+24g²) (-15g-18)

Then, take out the greatest common factor of both parenthesis.

4g² (5g+6) - 3 (5g+6)

You then separate the numbers outside the parenthesis and the numbers in the parenthesis.

(5g+6) (4g²-3)

Then you simplify the second set of numbers. Since the set of numbers can't be simplified, you would leave this problem as it is. I hope this makes sense.