A water tower containing 4000 m3 of water has been taken out of service to install a chlorine monitor. The concentration of chlorine in the water tower was 2.0 mg/L when the tower was taken out of service. If the chlorine decays by first-order kinetics with a rate constant k=1.0 d-1, what is the chlorine concentration when the tank is put back in service 8 hours later? What mass of chlorine (in kg) must be added to the tank to raise the chlorine level back to 2.0 mg/L? You may assume the tank is a completely mixed batch reactor.