Use Back-Substitution to Solve the System of Linear Equations $\left\{ \begin{array} { c c c } 4 x - 3 y - 2 z & = & 21 \\6 y - 5 z & = & 5 \\z & = & - 7\end{array} \right.$

Multiple Choice

Use back-substitution to solve the system of linear equations. $\left\{ \begin{array} { c c c } 4 x - 3 y - 2 z & = & 21 \\6 y - 5 z & = & 5 \\z & = & - 7\end{array} \right.$

A) $( - 2 , - 5 , - 7 )$
B) $( - 2,5,7 )$
C) $( - 5,7 , - 2 )$
D) $( - 2 , - 5,7 )$
E) $( - 5 , - 7 , - 2 )$