algebra
posted by lisa on .
The atmospheric pressure P in pounds per square inch (psi) is given by
P = 14.7 e^−0.21 a
where a is the altitude above sea level (in miles). If a city has an atmospheric pressure of 12.17 psi, what is its altitude?

you are solving
12.17 = 14.7 e^(.21a)
.827891156 = e^(.21a)
ln (.827891156) = .21a lne
.21a = .188873...
a = appr .8994 miles or appr 4750 ft to the nearest ten feet.