I need C. Only

Check m A random sample of 25 items is drawn from a population whose standard deviation is unknown. The sample mean is I = 850 and the sample standard deviation is s = 15. Use Appendix D to find the values of Student's t. (a) Construct an interval estimate of / with 95% confidence. (Round your answers to 3 decimal places.) The 95% confidence interval is from 843.808 to 856.192 (b) Construct an interval estimate of / with 95% confidence, assuming that s = 30. (Round your answers to 3 decimal places.) The 95% confidence interval is from 837.616 to 862.384 c) Construct an interval estimate of / with 95% confidence, assuming that s = 60. (Round your answers to 3 decimal places.)