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)? A thermometer reading 22° Celsius is placed in an oven preheated to a constant temperature. Through a glass window in the oven door, an observer records that the thermometer read 32° after 29 seconds and 37° after 58 seconds. How hot is the oven?