Convert both amounts to gallons and add:

$\displaystyle\frac{{{2}\ \text{ quarts}}}{{1}}\cdot\frac{{{1}\ \text{ gallon}}}{{{4}\ \text{ quarts}}}=\frac{{1}}{{2}}\ \text{ gallon}\usepackage{cmbright}\Huge\$

$\displaystyle\frac{{{8}\ \text{ pints}}}{{1}}\cdot\frac{{{1}\ \text{ quart}}}{{{2}\ \text{ pints}}}\cdot\frac{{{1}\ \text{ gallon}}}{{{4}\ \text{ quarts}}}={1}\ \text{ gallon}\usepackage{cmbright}\Huge\$

$\displaystyle\frac{{1}}{{2}}+{1}={1}\frac{{1}}{{2}}\ \text{ gallons}\usepackage{cmbright}\Huge\$