Final answer:
The percentage of oxygen in the air sample, after subtracting 75.56% of nitrogen from 100%, would be around 21%, accounting for the typical atmospheric composition, although this may vary with altitude. The pressure at 30,000 feet is about 0.25 atm, considering that pressure decreases by half approximately every 18,000 feet.
Step-by-step explanation:
To calculate the percentage of oxygen in the air sample at 30,000 feet with a given composition of 75.56% nitrogen, one will need to know the typical composition of air. Assuming no other gases are present in significant quantities, one can subtract the percentage of nitrogen from 100% to find the percentage of oxygen and other trace gases, which is typically around 21% oxygen in Earth's atmosphere at sea level. However, the composition can vary slightly with altitude. To determine the pressure of the air sample at 30,000 feet, one would need to consider how air pressure decreases with altitude. The atmospheric pressure decreases approximately by half every 18,000 feet, so at 30,000 feet, it would be around 1/4 of the atmospheric pressure at sea level, thus approximately 0.25 atm.