4. [2] An oil tanker aground on a reef is forming a circular oil slick about 0.2 foot thick. To estimate the rate dV/dt (in cubic feet per minute) at which the oil is leaking from the tanker, it was found that the radius of the slick was increasing at 0.25 foot per minute when the radius R was 600 feet. Find 0' V/dr. Round answer to the nearest whole number