Atank originally contains 100gal of fresh water. then water containing 12 lb of salt is poured into the tank at a rate of 2 gal/min, and the mixture is allowed to leave at the same rate. after 10 min the process is stopped, and fresh water is poured into the tank at a rate of 2 gal/min, with the mixture again leaving at the same rate. find the amount of salt in the tank at the end of an additional 10 min.