Solve the Equation by Expressing Each Side as a Power $$\mathrm { e } ^ { \mathrm { x } + 9 } = \frac { 1 } { \mathrm { e } ^ { 3 } }$$

Multiple Choice

Solve the equation by expressing each side as a power of the same base and then equating exponents.
- $$\mathrm { e } ^ { \mathrm { x } + 9 } = \frac { 1 } { \mathrm { e } ^ { 3 } }$$

A) $\{ - 12 \}$
B) $\{ 12 \}$
C) $\{ 6 \}$
D) $\{ - 6 \}$