Solve step by step.

3x * 10 - (9-0) * 5

First you need to distribute that invisible -1 to (9-0). You do this because of PEMDAS. -9+0 will be your outcome first. You can disregard the zero and now multiply 10 * -9 * 5 as these have no x variable. Multiplying all of those you get -450 * 3x. Thats the simplified form of this problem. -1350x if you're teachers looking for that.

This is an order of operations question so you would do the parenthesis first which would be 9-0 then multiplication would be either *5 or 3x*10 and the answer is -15x