A tank originally contains 100 gal of fresh water. Then water containing
lb of salt per
gallon 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
