The  management of a large store wishes to add a fenced-in r…

The  management of a large store wishes to add a fenced-in rectangular storage yard of 20,000 ft2 , using the building as one side of the yard.    Find the minimum amount of fencing that must be used to enclose the remaining three sides of the yard.   (Don’t forget to prove that it is a minimum!)       You MUST show ALL work/steps to get credit!    (Don’t type anything in this box)