A company plans to invest in a computer system to automate a process. The computer system will cost $30,000 and result in a labor savings of $45,000 per year. The operating cost of the system will be $5,000 per year and the system can be sold in 5 years for $3,000. How long does is take to recover the investment using discounted payback if the firms interest rate is 15%? use excel please if possible.