1. The problem statement, all variables and given/known data The problem states that we have a tank with a capacity of 400L filled with a mixture that has a concentration of 0.05g Chlorine per Liter. The concentration is reduced by pumping in pure water (zero concentration of chlorine), at a rate of 4L/s, and pumped out at 10L sec. 2. Relevant equations I know that the rate of change in concentration is equal to the rate in minus the rate out. 3. The attempt at a solution The rate of concentration input is zero since it's pure water, and I set the concentration of mixture out at x/(400-6t) since the volume is decreasing at some concentration at 6L per second due to the larger amount of mixture being pumped out. So the equation is then dx/dt=0.05-x/(400-6t), at least from what I understand. Then, using the Linear Differential EQ method, I found I(x)=(400-6t)^-6. Multiplying both sides of the equation, I get (400-6t)^2(dx/dt)+(400-6t)^-7x=0.05(400-6t). The left side is suppose to resemble the product rule, but I'm thinking I really messed something up at some point. Could someone point out my mistake so I can do a retake? Sorry if this is hard to read, I'm not good at inputting equations. Thanks for any help.