Determine whether the given value is a statistic or a parameter. A study was conducted of all 1575 workers in a certain state.

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.