What is the average rate of extra evaporation, in calories per minute, caused by the antipyrin drug in a 30 kg child running a temperature of 101°F, which is brought down to 98°F in 20 minutes, assuming the only heat loss mechanism is through evaporation? (The specific heat of human body is approximately the same as that of water, and latent heat of evaporation of water at that temperature is about 580 cal g ⁻¹ .)