In part of an agreement between cigarette agencies and the government, levels of nicotine in cigarettes are to be slowly reduced over time. A sample of 40 measurements conducted on one brad of cigarettes 10 years ago yielded an average of 32.9mg per cigarette with a sample standard deviation of 4.4 mg. A study done last month on 30 cigarettes of this brand yielded a sample mean of 30.6mg with sample standard deviation 5.1 mg. What type of test should be used to determine if the levels now are lower than what they were 10 years ago