A large tank at first has 50 gallons of a solution that is holding 10 lbs. of a chemical. Water is going through at a constant rate, and the mixture is going out at a constant rate. What will be the flow rate if 2 lbs. remains after 20 mins? I assume it's a differential eqns. problem. I think I should define x(t) as amount of chemical, so dx/dt = - x(t)/50 but I'm not really sure. Can somebody walk me through this?