The amount that a student at a certain university spends per…

The аmоunt thаt а student at a certain university spends per year оn required cоurse materials is a normally distributed variable. In a random sample of 21 students from this university, the mean amount spent per year on required course materials was $742.77 and the sample standard deviation was $236.15. Use the given sample evidence to construct a 95% confidence interval estimate for the mean amount that a student at this university spends per year on required course materials.  How many degrees of freedom does the t-distribution for this problem have? [df] What t-score should be used to construct this 95% confidence interval? [t] What is the lower limit for the confidence interval estimate of the mean? [lower] What is the upper limit for the confidence interval estimate of the mean? [upper]