The take away should be that it takes a lot of corn to make one tank of gas. Its worth doing some searching. Just look up the quantity of corn it takes to make a gallon of ethanol.
On purely a weight basis (assuming 1 pound of corn makes one pound of ethanol) you'd need 240 pounds of corn to fill a 30 gallon tank. Of course, converting corn into ethanol is not anywhere close to that efficient. And that doesn't include the energy needed to grow and transport the crop/fuel.