Correct. Solve for y, so that the equation is in the form $\displaystyle{y}={m}{x}+{b}\usepackage{cmbright}\Huge\$ .

Add $\displaystyle{4}{x}\usepackage{cmbright}\Huge\$ to both sides: $\displaystyle{36}{y}={4}{x}+{18}\usepackage{cmbright}\Huge\$

Divide both sides by 36: $\displaystyle{y}=\frac{{1}}{{9}}{x}+\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$

The line has a slope of $\displaystyle\frac{{1}}{{9}}\usepackage{cmbright}\Huge\$ . A line perpendicular to it will have a slope that is the negative reciprocal, so its slope is $\displaystyle-{9}\usepackage{cmbright}\Huge\$ .