Idk how people understand algebra me

To factor by a binomial, I like to use synthetic division (You can use long division but it is more work).

We are actually given a binomial because if -2 is a zero, the binomial is represented by (x- (-2)) or (x+2)

To use synthetic division,

-2 | 1  2  -9  -18
         -2   0   18

      1  0  -9    0

Therefore, you know the constants of the equation which is equal to

1x^2 +0x -9x +0

x^2-9x

The full equation is equal to (x+2)(x^2-9x)