A mechanic sells a brand of automobile tire that has a life expectancy that is normally distributed, with a mean life of 30,000 miles and a standard deviation of 2100 miles. He wants to give a guarantee for free replacement of tires that don't wear well. How should he word his guarantee if he is willing to replace approximately 10% of the tires? Click to view page 1 of the table. Click to view page 2 of the table. Tires that wear out by miles will be replaced free of charge. (Round to the nearest mid as needed.)