1. The problem statement, all variables and given/known data we have a tank with 400L of water with Cl, 0.02kg of Cl. Fresh water is pumped in at 4L/s and out at 10L/s. Find the amount of Cl in the tank as a function of t. 2. Relevant equations Use of differential equations 3. The attempt at a solution I set up V(t)=400-6t in Liters and seconds. then I want dy/dx=(rate in)-(rate out) for Cl flowing. But no Cl is coming in correct? So rate in ends up being zero, which confuses me because then everything ends up equalling zero from what I've done. If you want to see more of what I've done, please post. Am I wrong to say rate in is 0???