24 credit card holders are selected at random For each, their current credit card balance is recorde

24 credit card holders are selected at random For each, their current credit card balance is recorded The average for these 24 people is = $600 Assume that the current balance of all credit card holders follows a normal distribution with unknown mean?, and that a 853% confidence interval for? is found to be $600 ± 331 Find the standard deviation? of the population?