An average person takes 18 breaths per minute and each breath exhales 0.0016 m3 of air containing 4% CO2. At the start of a seminar with 300 participants, the room air contains 0.4% CO2. The ventilation system delivers 10 m3 of air per minute to the 1500-m3 room. Find an expression for the concentration level of CO2 in the room.