Kelly throws a dart at a circular dartboard of radius 3 feet. Let X and Y denote the location where the dart lands. Assume that -3 ≤ X ≤ 3 and -3 ≤ Y ≤ 3 and X2 + Y2 ≤ 9, i.e., the dart lands on the dartboard. Moreover, assume that the dart's location is Uniform on the dartboard, i.e.,
fX,Y(x,y) = l/(9π)
if x,y are on the dartboard, i.e., x2 + y2 ≤ 9,
and fX,Y = 0 otherwise.
Let D = √(X2 +Y2) be the distance from the dart to the center of the dartboard. Find E(D).