Answer
$a. $
$\left\{\begin{array}{l}
x+y-3z=8\\
y-3z=5\\
z=-1
\end{array}\right.$
$b.$
$(3,2,-1)$
Work Step by Step
$a. $
$\left\{\begin{array}{l}
x+y-3z=8\\
y-3z=5\\
z=-1
\end{array}\right.$
$b.$
Back substitute $z=-1 $ into
$y-3z=5$
$y-3(-1)=5$
$y+3=5$
$y=2$
Back substitute $z=-1,\ y=2 $ into
$x+y-3z=8$
$x+2-3(-1)=8$
$x+5=8$
$x=3$
Solution: $(3,2,-1)$
