40 is the total distance.
One piece is used to make a circle of radius r. So the circumference of this circle is 2*pi*r and its area is pi*r²
Now 40 - 2r*pi is used to make a square, so this thing is the perimeter of the square. The square has four sides which are equal, so we can consider that each side will be 10 - (1/2)r*pi
Now we want the area of the square which is Side*Side (10 - (1/2)r*pi)²
Now you add the area of the circle and the area of the square
pi*r² + (10 - (1/2)r*pi)²
gmat prep geo
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