A child running a temperature of `101^@F` is given an antipyrin (i.e. a medicine that lowers fever) which causes an increase in the rate of evaporation of sweat from his body. If the fever is brought down to `98^@F` in 20 min., What is the average rate of extra evaporation caused by the drug ? Assume the evaporation mechanism to be the only way by which heat is lost. The mass of the child is 30 kg. The specifric heat of human body is approximately the same as that of water, and latent heat of evaporation of water at that temperature is aout `580 cal g^-1`.