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Explanation:
Radius of circle B = xy
Diameter of circle B = 2xy (double the radius to get the diameter)
Radius of circle A = Diameter of circle B
Radius of circle A = 2xy
Use this radius to get the area of circle A
Area = pi*(Radius)^2
Area = pi*(2xy)^2
Area = pi*(2xy)*(2xy)
Area = pi*(2*2)*(x*x)*(y*y)
Area = pi*4*x^2*y^2
Area = 4pi*x^2y^2