The radius of a circular oil slick expands at a rate of 7 m/min. (a) How fast is the area of the oil slick increasing when the radius is 51 m? (Use symbolic notation and fractions where needed.) dA dt (b) If the radius is 0 at time t = 0, how fast is the area increasing after 5 min? (Use symbolic notation and fractions where needed.) dA dt = m²/min m²/min