[tex]\begin{gathered} \text{if the lines are perpendicular, the product of the slopes is -1} \\ m\times\frac{1}{3}=-1 \\ m=-3 \\ \\ y=-3x+b \\ \\ \text{ since (2,6) is on the line} \\ 6=-6(2)+b \\ 6=-12+b \\ 6+12=b \\ b=18 \\ \\ \text{ the equation is } \\ y=-3x+18 \end{gathered}[/tex]
