So, it starts off with 10 half gallons. 10*1/2 is 5, so in other words she put in 5 gallons and paid 15.26. As an equation it can be represented by 5x=15.26 where x is the cost of the gallons which is what we're trying to find. We can solve by using the division property of equality and divide both sides by 5. This gets us x=3.052. So, it costs $3.052 exactly for a gallon of gasoline.