please use appropriate equations and data to solve the problem

A storage tank is being used in a chemical plant to dampen fluctuations in the flow to a down- stream chemical reactor. The exit flow from this tank will be kept constant at 1.5 kg/s; if the instantaneous flow into the tank exceeds this, the level in the tank will rise, while if the instanta- neous flow is less, the level in the tank will drop. If the instantaneous flow into the storage tank is 1.2 kg/s, what is the rate of change of mass in the tank