Given the equation
[tex]-3y-x=0[/tex]To determine the slope, first write the equation in slope-intercept form (y=mx+b)
[tex]\begin{gathered} -3y-x=0 \\ -3y=x \\ y=-\frac{1}{3}x \end{gathered}[/tex]The slope corresponds to the coefficient multiplying x.
For this equation the slope is equal to -1/3.