A large tank contains 110 litres of water in which 19 grams of salt is dissolved. Brine containing 11 grams of salt per litre is pumped into the tank at a rate of 7 litres per minute. The well mixed solution is pumped out of the tank at a rate of 2 litres per minute. (a) Find an expression for the amount of water in the tank after t minutes. (b) Let x(t) be the amount of salt in the tank after t minutes. Which of the following is a differential equation for x(t)? In Problem #8 above the size of the tank was not given. Now suppose that in Problem #8 the tank has an open top and has a total capacity of 265 litres. How much salt (in grams) will be in the tank at the instant that it begins to overflow?