Statistics word problem - testing hypothesis

Fast Service, a chain of automotive tune-up shops, advertises that its personnel can change the oil, replace the oil filter, and lubricate any standard automobile in 15 minutes, on the average. The National Business Bureau received complaints from customers that service takes considerably longer. To check the fast service claim, the Bureau had service done on 21 unmarked cars. The mean service time was 18 minutes and the standard deviation of the sample was 1 minute. Use the .05 signficance level to check the resonableness of the fast service claim.