Multiply both sides by the common denominator 21:

$\displaystyle{21}\cdot\frac{{{x}+{2}}}{{7}}=\frac{{x}}{{21}}\cdot{21}\usepackage{cmbright}\Huge\$

$\displaystyle\frac{{21}}{{7}}\cdot{\left({x}+{2}\right)}={x}\cdot\frac{{21}}{{21}}\usepackage{cmbright}\Huge\$

$\displaystyle{3}{\left({x}+{2}\right)}={x}\usepackage{cmbright}\Huge\$ or $\displaystyle{3}{x}+{6}={x}\usepackage{cmbright}\Huge\$

$\displaystyle{2}{x}+{6}={0}\usepackage{cmbright}\Huge\$

$\displaystyle{2}{x}=-{6}\usepackage{cmbright}\Huge\$ , so $\displaystyle{x}=-{3}\usepackage{cmbright}\Huge\$