8. The developer for a new filter for filter-tipped cigarettes claims that it leaves less nicotine in (4 point the smoke than does the current filter. Because cigarette brands differ in a number of ways, he tests each filter on one cigarette of each of nine brands and records the difference between the nicotine content for the current filter and the new filter. The mean difference for the sample is 1.321 milligrams, and the standard deviation of the differences is s = 2.35 mg. a. Carry out a complete significance test at the 5% level. b. Construct a 90% confidence interval for the mean amount of additional nicotine removed by the new filter