Subtract 1 from both sides of the equation:

$\displaystyle{3}{x}+{1}-{1}={10}-{1}\usepackage{cmbright}\Huge\$ or $\displaystyle{3}{x}={9}\usepackage{cmbright}\Huge\$

Divide both sides of the equation by 3:

$\displaystyle\frac{{{3}{x}}}{{3}}=\frac{{9}}{{3}}\usepackage{cmbright}\Huge\$ or $\displaystyle{x}={3}\usepackage{cmbright}\Huge\$