The atmospheric pressure P in pounds per square inch (psi) is given by

P = 14.7 e^{ā0.21 a}where a is the altitude above sea level (in miles). If a city has an atmospheric pressure of 13.21 psi, what is its altitude? (recall 1 mile = 5,280 ft.)

The atmospheric pressure P in pounds per square inch (psi) is given by
P = 14.7 (eā0.21 a) where a is the altitude above sea level (in miles).
If a city has an atmospheric pressure of 11.21 psi, what is its
altitude? (Recall that 1 mi = 5,280 ft. Round your answer to the nearest
foot.)
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11.21 = 14.7*e^-0.21a
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e^(-0.21a) = 0.7626
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-0.21a = -0.2710
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a = 1.2906 miles
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a = 1.2906*5280 = 6814 feet