Let x be the width and let y be the length. To find the area, the formula is W*L.
The width is 7 less than the length: x = y-7
We only want one variable to deal with first, so we could also write:
y = x+7
Then we have,
x*(x+7) = 170
x²+7x-170 = 0
(x+17)(x-10) = 0
So x = -17, 10
When x = -17, y = -17+7 = -10
When x = 10, y = 10+7 = 17
But we cannot have negatives so the first solution does not work.
The width is 10 and the length is 17.
