Solve the System of Equations by the Substitution Method $$\begin{aligned}y & = 5 x + 4 \\5 y - 15 x & = 30\end{aligned}$$

Multiple Choice

Solve the system of equations by the substitution method.
- $$\begin{aligned}y & = 5 x + 4 \\5 y - 15 x & = 30\end{aligned}$$

A) $\{ ( 1,9 ) \}$
B) $\{ ( 9,1 ) \}$
C) $\{ ( - 1,9 ) \}$
D) $\varnothing$