The question doesn't say whether 36" is the radius, diameter or circumference, so let's do 3 questions in one.
36" Radius
Area=(pi)*36^2=1296(pi)=4071.5sq in.
36" Diameter
Area=18^2(pi)=1017.9sq in.
36" Circumference
2(pi)r=36, so r=18/(pi).
Area=(pi)(18/(pi))^2=324/(pi)=103.13sq in.