Any automotive site can tell you how big the tank is, just take that number and multiply by the cost/gallon... really simple. Very very VERY simple.
The tank is 13.7 gallons. Most people will fill it up at 12 or 12.5 gallons. Some way before that, like at 10 gallons, and that makes the math really easy.
So 10 times whatever the price is. See? Simple.
Miles per gallon literally means how many miles you can drive on ONE gallon of gas. For us it's about 27 average. So if you put exactly one gallon in your tank, you'll be able to drive roughly 27 miles. Depending on where and how you drive that number can go up or down.
This really is second grade stuff here.