Can anyone help me with my abstract algebra homework?

[____]

I am having a diffcult problem with my homework. I have three questions that I need help with.

1..-->For all integers a and b, - (a+b) = (-a) + (-b)

2-->If a +c < b + c, then a < b

3-->For n > 0, 2 +2(2) + 2(3) + …+ 2(n) = 2(2(n)- 1)
(__) means subscript

Thanks