Answer:
x + 18 + 28/x
Step-by-step explanation:
You first have to factor the expression that represents the area using the AC method.
When done factoring, you should get the expression (x + 4)(x + 7).
From there you divide that by x + 7 to get the length
(x + 4)(x + 7) / x + 7 = x + 18 + 28/x.
This may not be the correct answer, but I believe this is correct.
If you wish to do it quicker, you can just divide the entire expression of the area by the expression of the length, but if you were writing it down on paper, I suggest factoring it out.
