The Radius of a Circular Puddle Is Growing at a Rate

Multiple Choice

The radius of a circular puddle is growing at a rate of $8 \frac { \mathrm { cm } } { \mathrm { s } }$ . How fast is the area growing at the instant when it equals 20 cm² Round your answer to the nearest whole number.

A) $127 \frac { \mathrm { cm } ^ { 2 } } { \mathrm {~s} }$
B) $1005 \frac { \mathrm { cm } ^ { 2 } } { \mathrm {~s} }$
C) $3 \frac { \mathrm { cm } ^ { 2 } } { \mathrm {~s} }$
D) $72 \frac { \mathrm { cm } ^ { 2 } } { \mathrm {~s} }$
E) $63 \frac { \mathrm { cm } ^ { 2 } } { \mathrm {~s} }$