How do you write an equation in standard form for a line which passes through (5, -8) m=1/2?

$y - {y}_{0} = m \left(x - {x}_{0}\right)$ to get:
$y - \left(- 8\right) = \frac{1}{2} \left(x - 5\right)$
$y = \frac{x}{2} - \frac{5}{2} - 8$
$y = \frac{x}{2} - \frac{21}{2}$
$2 y = x - 21$
$\textcolor{red}{x - 2 y = 21}$