A random sample of 23 items is drawn from a population whose standard deviation is unknown. The sample mean is c = 840 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 98% confidence. (Round your answers to 3 decimal places.) The 98% confidence interval is from to (b) Construct an interval estimate of / with 98% confidence, assuming that s = 30. (Round your answers to 3 decimal places.) The 98% confidence interval is from to