Chapter 3.3, Problem 11E

During the summer the temperature inside a van reaches ${55}^{\circ }\text{C}$, while that outside is a constant ${35}^{\circ }\text{C}$. When the driver gets into the van, she turns on the air conditioner with the thermostat set at ${16}^{\circ }\text{C}$. If the time constant for the van is $1/\text{K}=2\text{hr}$ and that for the van with its air conditioning system is $1/\text{K1}=\text{1/3}\text{hr}$, when will the temperature inside the van reach ${27}^{\circ }\text{C}$?