Solve the Problem $7 \mathrm {~mm} 2 / \mathrm { s }$

Solve the problem.
-Water is falling on a surface, wetting a circular area that is expanding at a rate of $7 \mathrm {~mm} 2 / \mathrm { s }$ . How fast is the radius of the wetted area expanding when the radius is $152 \mathrm {~mm}$ ? (Round your answer to four decimal places.)

A) $0.0147 \mathrm {~mm} / \mathrm { s }$
B) $0.0461 \mathrm {~mm} / \mathrm { s }$
C) $136.4348 \mathrm {~mm} / \mathrm { s }$
D) $0.0073 \mathrm {~mm} / \mathrm { s }$