We use the t distribution to construct a confidence interval for the population mean when the underlying population standard deviation is not known. Under the assumption that the population is normally distributed, find t_/2,df for the following scenarios.(You may find it useful to reference the t table.Round your answers to 3 decimal places.)

t_/2,df a. A 95% confidence level and a sample of 18 observations. b. A 99% confidence level and a sample of 18 observations. c. A 95% confidence level and a sample of 9 observations. d. A 99% confidence level and a sample of 9 observations.