Answer:
60ft
Step-by-step explanation:
Let's x, y be the width and length of the surrounding rectangle. Since the area is 450 sq feet, this means xy = 450 or y = 450/x
The perimeter of this rectangle is (since there are 3 sides only)
f(x,y) = 2x + y
This is something we need to minimize. We can start by substituting y = 450/x
f(x) = 2x + 450/x
Let's take the first derivative of this function and set it to 0
y = 450 / 15 = 30ft
so the minimum perimeter that needs taping over is
f(x,y) = 2x + y = 2*15 + 30 = 60ft