A tank containing 10 kg of salt dissolved in 1000 L of water has two salt solutions pumped in. The first solution of 0.2 kg salt/L is pumped in at a rate of 20 L/min and the second solution 0.05 kg salt/L is pumped in at a rate of 5 L/min. The tank drains at 25 L/min. Solve the salt concentration as a function of time t. 8. The liquid base of an ice cream has an initial temperature of 90 oC before it is place in a freezer with a constant temperature of -20 oC. After 1 hour, the temperature of the ice-cream base has decreased to 55 oC. Solve the temperature of the ice cream as a function of time t.