A girl purchased a mobile home last year. She has been suffering severe allergic symptoms and has detected a strong odor of formaldehyde. An analysis of the mobile home air has revealed that the formaldehyde concentration is 0.28 ppm, the ventilation number is 0.56 air changes per hour. She is recommended to increase the ventilation rate to reduce the formaldehyde concentration below the threshold odor level of 0.05 ppm. Assuming the mobile home volume is 148 m3 and that the outdoor air concentration is 0. Estimate the ventilation number required to achieve the threshold odor level. (Assume no decay of formaldeh