Your solutions would be x = -6 or x = 3.
To find the solutions of this equation you must first factor it by finding factors of -18 that have a difference of 3. This gives you:
(x + 6)(x - 3) = 0
If you set each bracket equal to 0, you can solve for x by either adding 3 or subtracting 6 and get x equal to -6 or 3.
I hope this helps!