Solve the System by the Substitution Method $$\left\{ \begin{array} { l } x + y = - 7 \\x - y = 15\end{array} \right.$$

Solve the system by the substitution method.
- $$\left\{ \begin{array} { l } x + y = - 7 \\x - y = 15\end{array} \right.$$

A) $\varnothing$
B) $\{ ( 4 , - 11 ) \}$
C) $\{ ( x , y ) \mid x + y = - 7 \}$
D) $\{ ( 4,11 ) \}$