Quality control studies for Dependable Dishwashers show the

Quality control studies for Dependable Dishwashers show the lifetime of a dishwasher follows a normal distribution with mean mu = 8 years and standard deviation sigma = 1.2 years. The company will replace any dishwasher that fails during the guarantee period. How long should the company\'s dishwashers be guaranteed if the company wishes to replace no more than 2% of the dishwashers?