题目

Compared with the previous week, air quality in Shanghai became worse last week , according to the latest report from the Shanghai Environment Monitoring Centre．        The average air pollution index （API） for sulphur dioxide （SO2） remain almost unchanged from the previous week, but the APIs for nitrogen oxide （NOx） and total suspended （悬浮） particles （TSP） rose by 35 and 27 percent．        The overall quality still belonged to class 2 category．Nitrogen oxide, caused mainly by vehicle exhaust and burning of cooking gas, was still the major pollutant of一个多边形的周长为158cm，所有各边长成等差数列，公差为3cm，最大边长为44cm，求多边形的边数．