9.68 Write H0 and Ha For each of the following scenarios, define the parameter of interest and appropriate null and alternative hypotheses.

a. To motivate more fathers to take a parental leave, the government of Austria extended child care benefits for two more months if the father stays home for that time. Now, a study wants to investigate whether more fathers stayed home compared to the 15% before the incentive was available.

b. To curb CO2 emissions, the government of Austria subsidized the purchase of green vehicles. Now, a study wants to investigate whether the average CO2 emissions from cars purchased last year has dropped from the 160 g/km of 5 years ago.

c. The legal retirement age for female workers in Austria is 60. A study wants to assess whether the actual average retirement age of female workers is different from 60.