2(-3) - 5(9) equals -51.
First, simplify 2 x (-3) to get -6. (Make sure to exchange a and b in for the numbers). Your problem should look like: -6 - 5 x 9.
Second, simplify 5 x 9 to get 45. Your problem should look like: -6 - 45.
Third, simplify. Your problem should look like: -51, which is the answer.