Answer:
Let
x-------> the width of the patio
we understand that
region of the pool=40*60-----> 2400 ft²
vicinity of the patio=[(40+2x)*(60+2x)]-2400
place of the patio=2400 ft²
so
[(40+2x)*(60+2x)]-2400=2400
2400+80x+120x+4x²-4800=0
4x²+200x-2400=0------> divide by 4 both sides----> x²+50x-600=0
therefore
the answer is
x²+50x-600=0