If 2 gal of premium gasoline costs $7.86, how much would it cost to completely fill a tank whose capacity is 8-gal?
There are 4 lots of 2-gals in a 8-gallon tank
So you will need to pay 4 lots of $7.86 to fill the tank.
4 times $7.86 is $28 + $3.44
Answer: Cost is $31.44