Solve
-The Formula $\mathrm { P } = 14.7 \mathrm { e } ^ { 0.21 \mathrm { x } }$

Solve.
-The formula $\mathrm { P } = 14.7 \mathrm { e } ^ { 0.21 \mathrm { x } }$ gives the average atmospheric pressure $\mathrm { P }$ , in pounds per square inch, at an altitude $x$ , in miles above sea level. Find the elevation of a jet if the atmospheric pressure outside the jet is $7.5$ pounds per square inch.

A) $- 0.1$ miles
B) $- 3.2$ miles
C) $3.6$ miles
D) $71.0$ miles