An extensive property is a property of a substance that is dependent on the size or the amount of the substance in a system. Examples are number of moles, volume, energy, entropy, heat capacity, internal energy and mass. This would also be the same definition for extensive values. From the problem statement, the extensive values are the cost and price. These values have units of $ per gram which, obviously, dependent with the mass of the gasoline. The other values like the humidity, air pressure and the hardness are called intensive values since they are independent of the amount of the substance.
