A random sample of 50 smokers were questioned about the number of hours they sleep each day. The sample of smokers sleeps on average 7.5 hours per day with a standard deviation of 0.4 hours. We want to test the hypothesis that smokers need less sleep than non-smokers, who need an average of 7.7 hours of sleep. Perform the test at a (a) 25%, (b) 10%, (c) 5% and a (d) 1% level of significance.