The x-intercept of the line is the point $\displaystyle{\left({x},{0}\right)}\usepackage{cmbright}\Huge\$ on the line. If $\displaystyle{y}={0},\usepackage{cmbright}\Huge\$ then $\displaystyle{5}{\left({0}\right)}+{3}{x}={12},\usepackage{cmbright}\Huge\$ so $\displaystyle{3}{x}={12}\usepackage{cmbright}\Huge\$ and therefore, $\displaystyle{x}={4},\usepackage{cmbright}\Huge\$ so the x-intercept is $\displaystyle{\left({4},{0}\right)}.\usepackage{cmbright}\Huge\$