The U.S. Department of Transportation requires tire manufacturers to provide preference information on tire sidewalls to help prospective buyers make their purchasing decision. One very important piece of information is the tread ware. A tire with a grade of 200 should last twice as long, on average as a tire with a grade of 100. A consumer organization wants to test the actual tread ware index of a brand name of tires that claims "graded 200" on the sidewall of the tire. A random sample of n=18 indicates a sample mean tread ware index of 195.3 and a sample standard deviation of 21.4. Is there evidence that the population mean tread ware index is different from 200? (use a 0.05 level of significance)

(Can you please try to do it in many steps with explanation, so I can also figure out how to solve similar questions, thank you!)