Kerosene heaters that are used for indoor heating are known to produce NO2, a highly toxic gas. NO2 poses a health hazard to people living in the household. Formulate a model to develop an expression for the change in NO2 concentration as a function of time. When the heater is on, it generates NO2 at a constant rate of SA moles per unit time. Ventilation air coming from the outside of the house at a volumetric flow Q contains no NO2 whereas the exit ventilation (also at the volumetric flow Q) will carry away NO2 at a concentration equal to that in the house. Here we assume that the air in the house is perfectly mixed. Assume that NO2 decomposes spontaneously with a first order reaction rate constant k (time-1).