# A spherical iron ball 10 cm in radius is coated with a layer of ice of uniform thickness that melts at a rate of $50\; cm^2/min$. When the thickness of ice is 15 cm, then the rate at which the thickness of ice decreases, is :
( A ) $\frac{1}{18 \pi} cm/min$
( B ) $\frac{1}{54 \pi} cm/min$
( C ) $\frac{1}{36 \pi} cm/min$
( D ) $\frac{5}{6 \pi} cm/min$