alegbra question on roots multiple choice?

I believe that what you are asked to do is use the principle that helps you find the next root, starting with the one solution given to you, therefore, what you do is long division, or synthetic division to find the missing root:

x2 + 3x - 18 divided by ( x - 3), or (x-a), which is the algebraic principle to find the next root.

If you apply the division you get the remainder (x + 6) and when you make this equal to zero, you come up with the answer x= -6

CHOICE 3

ANSWER

x^2 + 3x - 18 = 0
x^2 + 6x - 3x - 18 = 0
(x^2 + 6x) - (3x + 18) = 0
x(x + 6) - 3(x + 6) = 0
(x + 6)(x - 3) = 0

x + 6 = 0
x = -6

x - 3 = 0
x = 3

∴ x = -6 , 3
(option 3)

x² + 3x - 18 = 0
(x - 3)(x + 6) = 0
x = 3 , x = - 6

OPTION 3

-6

x²+3x-18=0
(x-3)(x+6)=0
x=-6 and 3

If one of the roots is 3, the other would be -6 because
(3)(-6) = 18

(x-3)(x+6)=x^2-3x+6x-18 = x^2 +3x -18