Young-hee is considering to buy CAA a new aircraft. She must choose between two types of aircraft. A plane that will be in effect for 10 years must immediately pay 400 billion to buy up every year to pay 400 million a year after the Korean won, the Korean won. The plane B, must immediately pay 300 million Korean won is said to be, in effect for seven years, since buying one year after year also is said to be attached to 9 billion Korean won of the cost of maintenance. Suppose an annual increase of using cash flow the same income arising from two planes, repeated on every planes useful life after the end of its purchase of the same type of aircraft. Young-hee should be assuming that the rate of return on investment needed to purchase two planes for 10 %. Where to buy a plane?