1. An airplane is flying high enough that the cabin pressure is 8.7 lb/in2. What is the minimal percentage of oxygen that must be in the air mixture to support human life? Assume that sea level pressure is 14.7 lb/in2 and that the minimal percentage at sea level is 17%. State your answer rounded to the tenth of a percent.
2. The background sound level at your plant is 83.7 dBA. If a compressor generates a sound level of 87.4 dBA, what will the combined sound level be when the compressor is on? (State your answer to the nearest tenth of a dBA)