Suppose commute times in a large city are normally distributed and that 62.50% of commuters in this city take more than 21 minutes to commute one-way. If the standard deviation of such commutes is 6.2 minutes, what is the mean commute?

for normal distirbution we know that at(100-62.5 =37.5 perncentile) z score =-0.3186 therefore mean commute=X-z*std deviaiton =21-(-0.3186)*6.2 =22.98 ~ 23 minutes

Please explain how we got the zscore value from table