Though you correctly substituted the slope for m in $\displaystyle{y}={m}{x}+{b}\usepackage{cmbright}\Huge\$ , you made a mistake when you were finding b. After substituting $\displaystyle{\left(-{6},{1}\right)}\usepackage{cmbright}\Huge\$ for x and y, you may have mistakenly subtracted 4 instead of adding 4 to both sides of the equation.