Solve the System by the Addition Method $$\left\{ \begin{array} { l } 7 x - 2 y = 6 \\- 21 x + 6 y = - 24\end{array} \right.$$

Multiple Choice

Solve the system by the addition method. If there is no solution or an infinite number of solutions, so state. Use set
notation to express the solution set.
- $$\left\{ \begin{array} { l } 7 x - 2 y = 6 \\- 21 x + 6 y = - 24\end{array} \right.$$

A) $\{ ( 7,6 ) \}$
B) $\{ ( 3,4 ) \}$
C) no solution; $\varnothing$
D) $\left\{ \left( \frac { 7 } { 9 } , - \frac { 2 } { 9 } \right) \right\}$