How do you simplify -7(5-12),7(-3-(-5+9),12(-8+2)? show work!

Times by the outside number than add/subtract 

First problem:
-7(5-12) Write the problem.
-7(-7) Subtract within parentheses.
49 Multiply, and due to both being negatives its a positive answer.

Second problem:
7(-3-8) Write the problem.
7(-11) Subtract within parentheses.
-77 Multiply, due to one being negative its a negative answer.

Third problem:
-6(-5+9) Write the problem.
-6(4) Add within parentheses.
-24 Multiply, due to one being negative its a negative answer.

Fourth problem:
12(-8+2) Write the problem.
12(-6) Add within parentheses.
-72 Multiply, due to one being negative its a negative answer.

I hope this helps you understand simplifying these sort of problems! :D