A Sample of size n = 89 has sample mean x̄ = 87.2 and sample standard deviation s = 5.3.

1. Construct a 95% confidence interval for the population mean ?.

2. b. If the confidence level were 99%, would the confidence interval be narrower or wider?

( I am having trouble figuring out how the t-critical value of 1.963 is calculated as the answer for (a) and t-critical value for b)