[tex]\huge\boxed{\frac{3}{8}}[/tex]
To get the slope of a line from its standard form ([tex]Ax+By=C[/tex]), we can use [tex]m=-\frac{A}{B}[/tex].
[tex]\begin{aligned}m&=-\frac{A}{B}\\&=-\frac{3}{-8}&&\smash{\Big|}&&\text{Substitute in the known values.}\\&=\boxed{\frac{3}{8}}&&\smash{\Big|}&&\text{The negatives cancel out.}\end{aligned}[/tex]
Alternatively, we could have changed the equation to slope-intercept form and found the slope from there.