I'm assuming the 3.4's units are gallons, too. If you're rounding to the nearest <em>whole gallon</em>, that means you're going to have round 3.4 to the nearest <em>whole number. </em>Think about the two whole numbers 3.4 lies between: 3 and 4. Which one of those is 3.4 closer to? That's where you'll want to round.