Application of Differential Equation(mixing problem): A tank initially contains 100 L of a well-mixed water-and-salt solution, with salt concentration of 20 kg in the solution. If the solution is...

Application of Differential Equation(mixing problem): A tank initially contains 100 L of a well-mixed water-and-salt solution, with salt concentration of 20 kg in the solution. If the solution is exiting from the tank at a constant rate of 2 L per minute, what is the concentration of the salt (kilograms) in the solution at the point when the tank now only contains 50 L of the solution?