you usually get four prices for four different gasoline's you can pump. 
ex. 
unleaded =3.89
unleaded plus =3.99
unleaded premium =4.55
diesel #2= 4.65
so  unleaded gas is $3.89 per gallon of gas. 
so if you got 5 gallons of gas it would be 5 times$3.89 
[tex]5 \times 3.89[/tex]
these prices are just an example.