[tex]\begin{gathered} \text{ Since the slope is -1/}3\text{, the equation is} \\ y=-\frac{1}{3}x+b \\ \\ \text{now, it passes through (3,-9)} \\ -9=-\frac{1}{3}(3)+b \\ -9=-1+b \\ -9+1=b \\ b=-8 \\ \\ \text{ the equaiton is} \\ y=-\frac{1}{3}x-8 \end{gathered}[/tex]
