A large mixing tank initially contains 1000 gallons of water in which 40 pounds of salt have been dissolved. Another brine solut
ion is pumped into the tank at the rate of 5 gallons per minute, and the resulting mixture is pumped out at the same rate. The concentration of the incoming brine solution is 3 pounds of salt per gallon. If A(t) represents the amount of salt in the tank at time t, the correct differential equation for A is Select the correct answer
