A random sample of 14 items is drawn from a population whose standard deviation is unknown. The sample mean is x x = 780 and the sample standard deviation is s = 5. 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.) (b) Construct an interval estimate of with 98% confidence, assuming that s = 10. (Round your answers to 3 decimal places.) (c) Construct an interval estimate of with 98% confidence, assuming that s = 20. (Round your answers to 3 decimal places.) (d) Describe how the confidence interval changes as s increases