Himwood has 1200 ft2 of roof in his home in pittsburgh, pa (hdd = 6,000). he is considering upgrading the insulation from r-16 to r-22. the estimate from the contractor was $520. his home is heated with natural gas. last year, the average price he paid for natural gas was $13.3/mcf. assuming an afue of 82.2%, how long will it take himwood to recover his investment?