An office building and its equipment are insured to $710,000.The present annual insurance premium is $0.85 per $100 of coverage.A sprinkler system with life of 20 years and no salvage value can be installed for $18,000.Annual maintenance and operating costs for the sprinkler is $360. The premium will be reduced to $0.40 per $100 coverage if the sprinkler is installed. Find the payout period for sprinkler system with interest of 12%.