Solve the Problem $\mathrm { P } = 14.7 \mathrm { e } ^ { - 0.21 \mathrm { x } }$

Solve the problem.
-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 average atmospheric pressure for an altitude of $2.3$ miles. Round your answer to the nearest tenth.

A) $7.8 \mathrm { lb } / \mathrm { in } ^ { 2 }$
B) $9.1 \mathrm { lb } / \mathrm { in } ^ { 2 }$
C) $8.4 \mathrm { lb } /$ in. $^ { 2 }$
D) $11.0 \mathrm { lb } /$ in. $^ { 2 }$