Solve the System of Equations by the Substitution Method $$\left\{ \begin{array} { r r } x + 6 y & = 7 \\- 4 x + 7 y & = - 28\end{array} \right.$$

Solve the system of equations by the substitution method.
- $$\left\{ \begin{array} { r r } x + 6 y & = 7 \\- 4 x + 7 y & = - 28\end{array} \right.$$

A) $( - 7 , - 1 )$
B) $( 7,0 )$
C) $( 8,7 )$
D) $\varnothing$