Factor z2 – 3z – 18.
a. (z + 2)(z – 9)
b. (z + 3)(z – 6)
c. (z – 3)(z – 6)
d. (z + 8)(z – 10)

Your answer for this will be B (z+3)(z-6). Since the original equation has two negatives, the answer has to have one positive and one negative so the negatives don't cancel each other out and create a positive. To find the numbers in the parenthesis, you need to find something that multiplies to -18 and also adds to -3 at the same time. Choice B is correct because -6x3=-18 and -6+3=-3.