In a study of differences in levels of community demand for firefighters, the following sample regression was obtained, based on 46 towns in Bavaria, Germany:

yn = -0.00178 - 0.00035x1 10.000102

- 0.00002x2 10.0000162

+ 0.00036x3 10.000142

+ 0.52569x4 10.686482

+ 0.05146x5 10.013672

- 0.00009x6 10.000042

+ 0.00743x7 10.003482 R2 = 0.3572 where y = number of full-time firefighters per capita x1 = maximum base salary of firefighters, in thousands of euro x2 = percentage of population x3 = estimated per capita income, in thousands of euro x4 = population density x5 = amount of intergovernmental grants per capita, in thousands of euro x6 = number of miles from the regional city x7 = percentage of the population that is male and between 12 and 21 years of age The numbers in parentheses under the coefficients are the estimated coefficient standard errors.

a. Find and interpret a 99% confidence interval for b5.

b. Test, against a two-sided alternative, the null hypothesis that b4 is 0, and interpret your result.

c. Test, against a two-sided alternative, the null hypothesis that b7 is 0, and interpret your result.