This is a multiplication of fractions. If the tank is 3/4 full, and the tank holds 14.5 gal, then we need to multiply 14.5 * 3/4 First, convert 14.5 to 14 1/2 = 29/2 as an improper fraction Now, we have 29/2 * 3/4 = 87/8 = 10 7/8 gal That's how much gas is in the tank now. However, we want to know how much is needed to fill the tank. That can be determined by subtracting 10 7/8 from the amount that the tank can hold when full, which is 14.5 or 14 1/2. 14 1/2 - 10 7/8 can be re-written using improper fractions 29/2 - 87/8 We need a common denominator, which is 8 116/8 - 87/8 = 29/8 = 3 5/8 gal That's how much is needed to fill the tank