Solve the System of Equations by the Substitution Method $\begin{aligned}x + y & = 6 \\y & = 2 x\end{aligned}$

Multiple Choice

Solve the system of equations by the substitution method.
- $\begin{aligned}x + y & = 6 \\y & = 2 x\end{aligned}$

A) $\{ ( - 2,4 ) \}$
B) $\{ ( 2 , - 4 ) \}$
C) $\{ ( 2,4 ) \}$
D) $\{ ( - 2 , - 4 ) \}$