As part of an anemia treatment study in cattle, the researchers measured the selenium concentration in the blood of 26 cows treated with a selenium supplement (2 mg / day) for one year. All the cows were breeding (Santa Gertrudis). The average concentration of selenium was 6.21 g / dLi. Assume that the selenium concentration in the blood of cows is normally distributed with a standard deviation of 1.84 g / dLi (18 points). a. Between which two values does the population mean lie if I use a confidence level of 80%? b. Between which two values does the population mean lie if I use a confidence level of 92%? c. Between which two values does the population mean lie if I use a confidence level of 96%