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%. (The payout period is the length of time before the savings due to sprinkler system is equal its cost.) (Hint: find the time at which the present equivalent value of the cumulative net savings equals its cost $18,000)