A 200 gallon tank initially contains 100 gallons of water with 20 pounds of salt. A salt solution with pound of salt per gallon is added to the tank at 10 gallons per minute, and the resulting mixture is drained out at 5 gallons per minute. Let Q (t) denote the quantity (in pounds) of salt at time t (in minutes). I a. Write a differential equation for Q (t) which is valid up until the point at which the tank overflows. Q'(t) b. Find the quantity of salt in the tank as it's about to overflow. pounds