In Calm Waters the Oil Spilling from the Ruptured Hull

In calm waters the oil spilling from the ruptured hull of a grounded tanker forms an oil slick that is circular in shape. If the radius r of the circle is increasing at the rate of feet/minute t minutes after the rupture occurs. Find an expression for the radius at any time t. Hint: .
How large is the polluted area 30 minutes after the rupture occurred?

A) ;

B) ;

C) ;

D) ;