How much more do public colleges and universities charge out-of-state students for tuition per year? A random sample of 19 public colleges and universities listed at www.collegeboard.com yielded the following data for students entering as Freshmen in Fall $2013 .$ a) Create a $90 \%$ confidence interval for the mean difference in cost. Be sure to justify your procedure.
b) Interpret your interval in context.
c) A national magazine claims that public institutions charge state residents an average of $\$ 7000$ less than out-of-staters for tuition each year. What does your confidence interval indicate about this assertion?