A tank initially contains 50 gallons of brine, with 30 pounds of salt in solution. Water runs

Question:

A tank initially contains 50 gallons of brine, with 30 pounds of salt in solution. Water runs into the tank at 3 gallons per minute and the well-stirred solution runs out at 2 gallons per minute. How long will it be until there are 25 pounds of salt in the tank?