EXPLANATION
The relationship between quarts and gallons is as follows:
[tex]1\text{ gallon=4 quarts}[/tex]Therefore, we can apply the unit method in order to get the number of gallons:
[tex]Number\text{ of gallons=120 quarts*}\frac{1\text{ gallon}}{4\text{ quarts}}[/tex]Simplifying:
[tex]Number\text{ of gallons=30 gallons}[/tex]In conclusion, the solution is 30 gallons.