An accident at an oil drilling platform is causing a circular-shaped oil slick to form. the volume of the oil slick is roughly given v(r) = 0.07πr^2, where r is the radius of the slick in feet. in turn, the radius is increasing over time according to the function r(t) = 0.4t, where t is measured in minutes.

1) find (v of r)(t) and simply it