The national average for the number of students per teacher for all U. S. public schools is 15.9. A random sample of 12 school districts from a moderately populated area showed that the mean number of students per teacher was 19.2 with a variance of 4.41. Assume a normal distribution is appropriate for the number of students per teacher. a)[7 pts] Estimate the true mean number of students per teacher with 95% confidence from the random sample. b) [6 pts] A researcher makes the claim that moderately populated districts have a different number of students per teacher than the national average. Do the data support this claim