A large tank contains 450 liters of a salt solution which has a concentration of 0.4 kilograms per liter. Pure water is added to the solution at a rate of 60 liters per minute. At the same time, the solution drains from the tank at 60 liters per minute.

1. Find the amountSof the salt in the solution as a function oft:

2. At what time is there only 93 kilograms of salt remaining in the tank?