we know that
[length of a circumference]=2*pi*r
for r=9 yd
[length of a circumference]=2*pi*9-------> 56.52 yd
if 2*pi radians (full circle)--------------> has a length of 56.52 yd
pi/6 radians----------------------------> X
X=(pi/6)*56.52/(2*pi)-----> X=4.71 yd
the answer is
the arc length is 4.71 yd