A spherical balloon is filled with $4500 \pi$ cubic meters of helium gas. If a leak in the balloon causes the gas to escape at the rate of $72 \pi$ cubic meters per minute, then the rate (in meters per minute) at which theradius of the balloon decreases 49 minutes after the leakage began is
(A) $\frac{9}{7}$
(B) $\frac{7}{9}$
(C) $\frac{2}{9}$
(D) $\frac{9}{2}$