
Step by Step Step-by-step explanation:
The area a is defined as

Now take derivative of the above expression with respect to time:

Solving for dr/dt, we then get

Note that da/dt = 900 m^2/s and when the area of the oil slick is 1400 m^2, the radius r is r = √(1400/π) = 21.1 m. Therefore,the rate at which the radius is increasing dr/dt is
