Can someone help me with my math?

A big part of math is pattern recognition. A lot of homework is just fighting with stuff so you will remember the pattern when you see it again. The most common pattern is (x + a) * (x + b) = x^2 + (a + b)x + ab and the special case (x + a) * (x - a) = x^2 - a^2. When you spot the pattern you can just write the answer from memory.

Now study this page until it seems obvious: https://en.wikipedia.org/wiki/Polynomial_remainder_theorem

Given: 2x-18 I see two even numbers. Take out the 2.

2(x - 9) That's all I see.

2x - 18 = 2 x 2 = 18

2 (x - 9)