samson ltd is considering replaing equipment. the cost on 1.1.2023 will be $3 million. the expected economic life of the equipment will be 4 years. the company depreciates its equipment using the straight line method. the company expects to sell this equipment for $400,000 after the end of its useful economic life. there are expected cost savings arising from this investment of $1,200,000 in each of years 1 and 2 and $800,000 in each of years 3 and 4. what is the payback of this investment?