6. An asset purchased 2 years ago for $50,000 is harder to maintain than expected. It can be sold now for $15,000 or kept for a maximum of 3 more years, in which case its operating cost will be $20,000 each year, with a salvage value of $10,000 after 1 year or $9000 after two years. A suitable challenger will have $30,000 first cost. The operating cost will be $14,000 each year, with a salvage value of $5,000 after 6 years. At an interest rate of 10% per year, should the defender be replaced now, one year from now, two years from now, or three years from now