Early Monday morning, the temperature of a lecture hall has fallen to 40 degrees F, the same temperature as the outside. At 7:00 AM the janitor turns on the furnace with the thermostat set at 70 degrees F. The time constant for the building is 1/K = 2 hr and that for the building along with the heating system is 1/K1 = 1/2 hr. Assuming the outside temperature remains constant, what will be the temperature inside the lecture hall at 8:00 AM?
When will the temperature inside the lecture hall reach 65 degrees F?

I know that I have an expression for the heating Ku(70-T) but after that I am lost.

Thank you