If the System Has Infinitely Many Solutions, Write the Solution $$\begin{aligned}4 x + y + z & = 6 \\x - y + 2 z & = 12 \\4 x + y + z & = 21\end{aligned}$$

Multiple Choice

If the system has infinitely many solutions, write the solution set with x arbitrary.
- $$\begin{aligned}4 x + y + z & = 6 \\x - y + 2 z & = 12 \\4 x + y + z & = 21\end{aligned}$$

A) $\{ ( 4,5 , - 3 ) \}$
B) $\{ ( 4 , - 3,5 ) \}$
C) $\varnothing$
D) $\{ ( 5 , - 3,4 ) \}$