Subtract 2 from both sides of the equation to get 0 on one side:

$\displaystyle{21}{{x}}^{{2}}+{x}-{2}={0}\usepackage{cmbright}\Huge\$

$\displaystyle{\left({3}{x}+{1}\right)}{\left({7}{x}-{2}\right)}={0}\usepackage{cmbright}\Huge\$

$\displaystyle{3}{x}+{1}={0}\usepackage{cmbright}\Huge\$ or $\displaystyle{7}{x}-{2}={0}\usepackage{cmbright}\Huge\$

$\displaystyle{x}=\frac{{-{1}}}{{3}}\usepackage{cmbright}\Huge\$ or $\displaystyle{x}=\frac{{2}}{{7}}\usepackage{cmbright}\Huge\$