Answer
$x=\dfrac{-2y+z-13}{2}$
Work Step by Step
Using the properties of equality, in terms of $
x
$, the given equation, $
z=13+2(x+y)
$, is equivalent to
\begin{array}{l}
z=13+2x+2y
\\\\
-2x=13+2y-z
\\\\
x=\dfrac{13+2y-z}{-2}
\\\\
x=-\dfrac{13+2y-z}{2}
\\\\
x=\dfrac{-13-2y+z}{2}
\\\\
x=\dfrac{-2y+z-13}{2}
.\end{array}