The rectangle below has an area of x^2-16 square meters and a width of x+4 meters.
what expression represents the length of the rectangle?

X^2-16 is a difference of squares of the form:

(a^2-b^2) which always factors to:

(a+b)(a-b), in this case we have:

(x+4)(x-4), we are told that width is (x+4) so the length is:

(x-4)