The perimeter of a square is 80 - 64y. Which expression can be used to show the side length of one side of the square?
+73 since a square has 4 equal sides, the perimeter would be 4 * (side length of the square).
so, each side length of the square would be \(\frac{80-64y}{4}\).
80 / 4 = 20 and 64y / 4 = 16y
each side length of the square is 20 - 16y, or the third option.
it seems that you are asking many questions about factoring simple expressions. here is a site that may help:
https://www.factoring-polynomials.com/factoring-2.htm
i have mentioned this before, but Symbolab's simplifying calculators are helpful as well, in providing step-by-step solutions and tips. feel free to explore!
hope this helped! sorry if my explanations weren't that great. a quick search online will also always provide you with many resources and tips! 
