Elizabeth, this is easier than it looks. Let me give you an example. 7w means 7 times w, right?
Let's look at 5(6) + 6(6). That's 30 + 36 = 66, or 11(6).
In the same manner, 5w + 6w = 11w.
So, 7w - 3w + 4w = 8w. It's just like saying 7 oranges - 3 oranges + 4 oranges.
So, we have 8w = -15. We want to get the w by itself, and it's multiplied by 8, so the opposite is to divide by 8.
Remembering that we have to do the same to both sides, we get that w = -15/8, or w = -1 7/8.
