15x^3-12x
Begin with sorting out what 15x^3 and 12x have in common
15 and 12 are both divisible by 3, so divide 3 by both 15 and 12 and put 3 on the outside.
15x^3 and 12x also both have an x in common, so divide the x's (which is basically subtracting them).
3x(5x^2-4)
B
