Asalt solution having a concentration of cin = 2 pounds per gallon flows at a rate of ˙vin = 10 gallons per minute into a 125-gallon capacity tank, while the well-stirred solution is being pumped out at a rate of ˙vout = 5 gallons per minute. if the tank initially contained 500 pounds of salt dissolved in 50 gallons of water. when the amount of salt in the tank reach minimum?