The average daily metabolic rate for captive animals from weasels to elk can be expressed as a function of mass by r = 140.2m^0.75, where m is the mass of the animal (in kilograms) and r is the metabolic rate (in kcal per day).

(a) Suppose that the mass of a weasel is changing with respect to time at a rate dm/dt. Find dr/dt.
(b) Determine dr/dt for a 250-kg elk that is gaining mass at a rate of 2 kg per day.