Though you correctly substituted the slope 4 into $\displaystyle{y}={m}{x}+{b}\usepackage{cmbright}\Huge\$ , you then substituted the y-value, 5, from the ordered pair for b. Instead, you should substitute the coordinates of the point (8, 5) for x and y in $\displaystyle{y}={4}{x}+{b}\usepackage{cmbright}\Huge\$ and solve for b.