I’ll solve number 3.
You need to group the like terms. For example, -4n + 6n = 2n
8=2n
Now, we need to keep n by itself.
2n/2 = n
Whatever you do to one side, you need to do to the other.
8/2 = 4
So, in conclusion, n = 4.
I hope this helps for you to solve the rest!
