43 - w = 8 what does w equal. how?

43-w=8
-43    -43

-w= -35
you divide both -w and -35 to get rid of the negative signs or they crossed out so the answer is w=35

Since x is the length, then x+7 has to be the width.
The area of a rectangle can be found via the formula :
A = length * width
So if we replace the area with the given number (170) and the length, and width, with what we assumed, we get..
170 = x * (x+7)
[which is.. ]
170 = x^2 +7x
0 = x^2 +7x - 170

And that is the answer.