Answer:
 Javier can buy <em>at maximum</em> about 3.7 gallons of oil. 
Step-by-step explanation:
Let g represent the amount of gasoline in galloons. 
We know that Javier has at most $15.00 to spend. In other words, the total cost after buying the snacks and gasoline must be <em>less than or equal to </em>15. 
He already bought a snack and a drink for a total of $2.59. 
And each gallon of gasoline costs $3.39. 
So, we can write the following inequality: 

To find how many galloons of gasoline Javier can buy, we will need to solve for g. 
So, subtract 2.59 from both sides. This yields: 

Divide both sides by 3.39: 

So, Javier can buy <em>at maximum</em> about 3.7 gallons of oil. 
And we're done!