A certain brand of automobile tire has a mean life span of 34000 miles and a standard deviation of 2200 miles. (Assume the life spans of the tires have a bell-shaped distribution.)

(a) The life spans of three randomly selected tires are 35000 miles, 36000 miles, and 31000 miles. Find the z-score that corresponds to each life span. For the life span of 35000 miles, z-score is