We are told that 2 gallons cost $8.40. To determine how much a quarter of a gallon costs we need first find the price per gallon. To do that we divide the cost over the number of gallons, like this:
![N=\frac{8.40\text{ dollars}}{2\text{ gallon}}=4.20\text{ dollars/gallon}](https://img.qammunity.org/2023/formulas/mathematics/college/o68iyfvm2xl0yzop80ueofr1ryt2qernd1.png)
Now we multiply the price by 1/4 gallons:
![(4.20\text{ dollar/gallon)(1/4 gallon)=}1.05\text{ dollars}](https://img.qammunity.org/2023/formulas/mathematics/college/ogxrh0cjso4qxa70f95f8gqrcph367g12i.png)
therefore, a quarter gallon costs $1.05