To solve this algebraically, you can first factor out a 3:
[tex]3(x^2-2x-8)[/tex]
Then, you can factor (I'm using guess and check) and my answer is -4 and 2:[tex]3(x-4)(x+2)[/tex]
From here on, finding 0s is very easy. You just solve for x in the parentheses. So, the 0s are when x = 4, and x = -2. Remember, (4-4) = 0, and (-2+2) = 0, that's what you want.