Correct. Substitute the slope $\displaystyle-{4}\usepackage{cmbright}\Huge\$ into the equation $\displaystyle{y}={m}{x}+{b}\usepackage{cmbright}\Huge\$ : $\displaystyle{y}=-{4}{x}+{b}\usepackage{cmbright}\Huge\$

Substitute the coordinates of the point $\displaystyle{\left(-{3},{15}\right)}\usepackage{cmbright}\Huge\$ for x and y: $\displaystyle{15}=-{4}{\left(-{3}\right)}+{b}\usepackage{cmbright}\Huge\$

Solve for b: $\displaystyle{15}={12}+{b}\usepackage{cmbright}\Huge\$ , so $\displaystyle{3}={b}\usepackage{cmbright}\Huge\$

The y-intercept of the line is 3.