A sturl'lr has hcennade to compare the nicotine contents of taobmnds ofcigarettea. s cigarettes of Brand A had an average nicotine content of 4.: milligram .with a standard deviation of 0.5 milligram, whe eight cigarettes of Brand B had an average nicotine content of 27 miigranianith a standard deviation oft] 7 milligram Assuming that the two sets of data are independent random sample's from normal popudations with equal variations. construct a 95% condence interval for the : difference between the mean nicotine content: of the two brands of cigarettes