Thank your for calling World Airline . What can I do for you ?   I need to book a plane ticket to London .   Round-trip or one-way ?   One-way .   What date would you like to fly ?   Saturday , July 25 .   How many people will be traveling ?   Just one adult .   Which class ?   Economy , please . Economy class is the cheapest , right ?   Right . Ok , the fare is $ 700 . 