1. How did you get that answer for 1? are you sure you typed the problem correctly? becuase * means multiply, you would end up with

-60xb

2. Simplify -2x(x-3) + x(5-x)

First we expand the brackets for -2x(x-3) we multiply everything in the brackets by -2x to get -2x^2 + 6x, for the x(5-x) we multiply everything in the brackets by x to get 5x - x^2, so we end up with something like this

-2x(x-3) + x(5-x) = -2x^2 + 6x + 5x - x^2 = -3x^2 + 11x

3. I assume your question is: Multiply: a*2b - 3ab*2 +5b*3

by -2ab. Okay, can you clarify for me. do you use the * to mean a power? for example when you type a*2, do you mean a squared?