Barometric Pressure Halley's law states that the barometric pressure (in inches of mercury) at an altitude of x mi above sea level is approximated by the equation below.
$p(x) = 29.92e^{-0.2x}$ $(x \ge 0)$
If the barometric pressure as measured by a hot-air balloonist is 18 in. of mercury, what is the balloonist's altitude? (Round your answer to two decimal places.)
mi