A line passes through $\displaystyle{\left({3},{5}\right)}\usepackage{cmbright}\Huge\$ and $\displaystyle{\left(-{1},-{7}\right)}\usepackage{cmbright}\Huge\$ .

Find the y-intercept, b, of the line.

$\displaystyle{b}=\usepackage{cmbright}\Huge\$ _____