I don't get this. 3+7x-(2+9x) and also 6-(3x-4)+7x-11

The part I don't get is in the parenthesis I don't get how you can add 2 to 9x and 4 to 3x or the other ones. How do you add number to them please EXPLAIN and THANK YOU in advance.

you don't add them. i think it's there just to teach you about the importance of parenthesis. if there's a minus sign in front of the parenthesis, remember to switch the signs inside the parenthesis. so if it's a minus, then it becomes a plus sign when the parenthesis is removed.

3 + 7x - (2 + 9x) is the same as 3 + 7x - 2 - 9x.

6 - (3x - 4) + 7x - 11 is the same as 6 -3x + 4 + 7x - 11.

alright so the - sign in front of the parenthesis makes the numbers inside negative then you add and subtract everything. soo.......... 3+7x-(2+9x) -------> 3+7x-2-9X -----> 1-2x is your final answer. Then....... 6-(3x-4)+7x-11 ----> 6-3x+4+7x-11 ---> -1+4x is your answer

Distribute the negative sign in both so they read:
3+7x-2-9x and 6-3x+4+7x-11
they equal:
1-2x and 4x-1
Hope rhis helped :)

3+7x-(2+9x)
3+7x-2-9x
-2x+1

6-(3x-4)+7x-11
6-3x+4+7x-11
4x-1

e.g.
-(4x+2)
=>-1(4x); -1(2)
=>-4x-2