To add fractions with unlike denominators, you must rewrite them with a common denominator. You do not add the numerators and denominators.

$\displaystyle{2}\frac{{1}}{{6}}+{3}\frac{{11}}{{12}}={2}+{3}+\frac{{2}}{{12}}+\frac{{11}}{{12}}={5}+\frac{{13}}{{12}}={5}+{1}\frac{{1}}{{12}}={6}\frac{{1}}{{12}}\usepackage{cmbright}\Huge\$

The correct answer is $\displaystyle{6}\frac{{1}}{{12}}\usepackage{cmbright}\Huge\$ .