Avery large tank initially contains 100l of pure water. starting at time t = 0 a solution with a salt concentration of 0.4kg/l is added at a rate of 7l/min. the solution is kept thoroughly mixed and is drained from the tank at a rate of 5l/min. answer the following questions. 1. let y(t) be the amount of salt (in kilograms) in the tank after t minutes. what differential equation does y satisfy? use the variable y for y(t). answer (in kilograms per minute): 2. how much salt is in the tank after 30 minutes? answer (in kilograms):