You used the x-value and the y-value from the ordered pair as the coefficients of x and y in the equation $\displaystyle{y}={m}{x}+{b}\usepackage{cmbright}\Huge\$ . Then you replaced b with the slope, $\displaystyle-\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ , which is actually m in the equation.