pls help me answer asap this is rush thanks. Applications of ODE

2. A tank is filled with 20 gallons of brine in which is dissolved 3 Ibs of salt. Brine containing 3 Ibs of salt per gallon enters at 2 gallons per minute. The well-stirred mixture leaves at 1 gallon per minute. a. How many salt are there in the tank after 13.50 minutes? b. How long will it take in minutes for the salt in the tank to increase from 18.10 lbs to 32.50 lbs? c. How long will it take in minutes in minutes for the salt in the tank to be 50.2 lbs