An article in the Journal of the Electrochemical Society describes an experiment to investigate the low-pressure vapor deposition of polysilicon. The experiment was carried out in a large-capacity reactor at Sematech in Austin, Texas. The reactor has several wafer positions, and four of these positions are selected at random. The response variable is film thickness uniformity. Three replicates of the experiment were run and the data are as follows: Wafer Position Uniformity Uniformity Uniformity
1 2.76 5.67 4.49
2 1.43 1.7 2.19
3 2.34 1.97 1.47
4 0.94 1.36 1.65

Required:
a. Construct a 95% confidence interval for the true average compressive strength when rodding level is at 20.
b. Construct a 95% confidence interval for the true effect of rodding level upon compressive strength when rodding level is at 15.
c. Construct a 95% individual confidence interval for the true difference in the average compressive strength of rodding levels 15 and 25.