2a-5b; a=-3 and b=9

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.