Solve the System by the Addition Method $$\left\{ \begin{array} { r } 5 x + 6 y = - 7 \\- 5 x - 13 y = 21\end{array} \right.$$

Multiple Choice

Solve the system by the addition method.
- $$\left\{ \begin{array} { r } 5 x + 6 y = - 7 \\- 5 x - 13 y = 21\end{array} \right.$$

A) $\{ ( - 1,2 ) \}$
B) $\{ ( x , y ) \mid 5 x + 6 y = - 7 \}$
C) $\varnothing$
D) $\{ ( 1 , - 2 ) \}$