You have decided to ascend to the summit of Mount Everest, where the partial pressure of oxygen in the atmosphere has been estimated to be about 54 mmHg. Recall that when this air arrives in the alveoli, the partial pressure of oxygen drops even lower because of displacement by the partial pressure of carbon dioxide and water vapor. The arterial concentration of oxygen at the pulmonary capillaries is measured and found to be 25 mmHg. What is the percent saturation of hemoglobin at this partial pressure