Multiply both sides of the equation by 5:

$\displaystyle{5}\cdot\frac{{x}}{{5}}={5}\cdot{7}\usepackage{cmbright}\Huge\$ or $\displaystyle\frac{{5}}{{5}}\cdot{x}={35}\usepackage{cmbright}\Huge\$ or $\displaystyle{x}={35}\usepackage{cmbright}\Huge\$