A truck has purchased at 160000.the value of truck is depreciated in first three years by 20000 each year and Rs 16000 per year thereafter.its maintenance and operating costs for the first three years are Rs 16,000 Rs 18000 and Rs 20000 in that order and increased by Rs 4000 every year Assuming an interest rate of 10% find the economic life of truck...

Answer is 7 years but I want procedure to this problem