The excluded values of a rational expression are 0, 6, and 9. Which of the following could be this expression? a+6/a^3-15a^2-54a, a+6/a^2-15a+54, a^3-15a^2+54a/a+6, a+6/a^3-15a^2+54a

Arandom sample of 45 observations results in a sample mean of 68. the population standard deviation is known to be 23 a. compute the margin of error at a 959% confidence interval. b. compute the 95% confidence interval for the population mean c. compute the 90% confidence interval for the population mean. d. compute the 75% confidence interval for the population mean