Question 19402
You could try factoring the polynomial.

{{{x^2 - 3x - 18 = 0}}}  You need to find two integers whose product is -18 and whose sum is -3. (x + ? )(x + ?)

Try 3 X -6 = -18
3 + (-6) = -3
{{{(x + 3)(x - 6) = 0}}} = {{{x^2 - 3x - 18 = 0}}} So these are the correct factors.

{{{(x + 3)(x - 6) = 0}}} Apply the zero products principle.
(x + 3) = 0 and/or (x - 6) = 0
If x + 3 = 0 then, x = -3
If x - 6 = 0 then, x = 6

The roots are: 
x = -3
x = 6