The slope-intercept form of a line is $\displaystyle{y}={m}{x}+{b}\usepackage{cmbright}\Huge\$ , where m is equal to the slope of the line and b is equal to the y-intercept. You ignored the negative sign in the y-value of the given point $\displaystyle{\left({0},-{3}\right)}\usepackage{cmbright}\Huge\$ . This is the y-intercept of the line, so $\displaystyle{b}=-{3}\usepackage{cmbright}\Huge\$ , not 3.