The audiometry room used for an occupational hearing conserv…

The audiometry room used for an occupational hearing conservation program is scheduled for renovation. The renovated room will have 4 ducts for ventilation. Each duct will have one fan, and all fans must identical for effective ventilation. In order to obtain valid thresholds, the total noise of the fans must remain below 40 dBA. Assume that the noise from the duct fans radiates equally through the room. Which represents the max noise level that can be emitted from each individual fan?