Correct. Since the line $\displaystyle{y}=\frac{{1}}{{3}}{x}+{7}\usepackage{cmbright}\Huge\$ has slope $\displaystyle\frac{{1}}{{3}}\usepackage{cmbright}\Huge\$ , any line perpendicular to it will have slope -3 (the opposite reciprocal of $\displaystyle\frac{{1}}{{3}}\usepackage{cmbright}\Huge\$ ).