Timmy recorded the number of cricket chirps he heard in a minute on several different nights. He recorded the number of chirps, x, that he heard during each recording. The number of chirps observed was normally distributed with a mean of 54 and a standard deviation of 8.4.

Find the z – score that corresponds with the probability of observing at most 64 chirps during a night. Round your answer to the nearest tenth.

z = _{}