An adult usually breathes around 12 to 20 times per minute when at rest. If we consider the upper limit of this range to account for physical exertion, that would be 20 breaths per minute. To find the total number of breaths taken in a day, we can calculate 20 (breaths) * 60 (minutes) * 24 (hours), resulting in 28,800 breaths per day. However, it's important to recognize that this is just an estimate; the actual number can differ based on various factors such as physical activity level, lung capacity, and overall health.