Start with the initial fee which is $4. Then times 2 with your miles for an example: (money with miles)2 x 6(miles) and you should have $12 dollars in total 2 x 4 which equal $8 and 2x2 which equal 4...
10 liters of gas fill one tank. x liters of gas fill x/10 tanks. 35 liters of gas fills 35/10=7/2 tanks 7/2 can also be written as 3.5 or the mixed number (3 and 1/2)