The given line is written in the form $\displaystyle{y}={m}{x}+{b}\usepackage{cmbright}\Huge\$ . Since $\displaystyle{m}=-{3}\usepackage{cmbright}\Huge\$ , the slope is $\displaystyle-{3}\usepackage{cmbright}\Huge\$ . Perpendicular lines have slopes that are negative reciprocals of each other. Find the reciprocal of $\displaystyle-{3}\usepackage{cmbright}\Huge\$ , which is $\displaystyle-\frac{{1}}{{3}}\usepackage{cmbright}\Huge\$ , and change the sign. The slope is $\displaystyle\frac{{1}}{{3}}\usepackage{cmbright}\Huge\$ .