Alpha Castings Private Limited,a small scale industry purchases a generator for Rs. 20,000. The operation cost is Rs 2000 during the first year of its operation and it is increases by Rs 1000 every year thereafter. The maintenance cost is Rs. 200 during the first year of its operation and it is increased by Rs. 100 every year thereafter. The purchase of this generator is through an interest free loan sanctioned for this company by Small Scale industry Development Corporation. Find the economic life of the generator