Can someone please explain it to me ASAP??!!!

A tank initially contains 80 gal of pure water. Brine containing 5 lb of salt per gallon enters the tank at 2 gal/min, and the (perfectly mixed) solution leaves the tank at 3 gal/min. Thus, the tank is empty after exactly 80 min. (a) Find the amount of salt in the tank after t minutes (b) What is the maximum amount of salt ever in the tank? (80 -1)3 (a) The amount of salt x in the tank after t minutes is x = 5(80 -t) - 1280 (b) The maximum amount of salt in the tank was about 153.97 Ib. (Type an integer or decimal rounded to two decimal places as needed.)