When 60 convicted embezzlers were randomly selected, the mean length of prison terms was found to be 21.3 months and the standard deviation was 8.1 months. A woman is running for political office on a platform of tougher treatment of convicted criminals. Test her claim that prison terms for convicted embezzlers have a mean of less than 24 months. Use a 0.05 significance level.

What is the z-score?