The Credit Counselling and Debt Management Agency (AKPK) is concerned about the increase in the level of credit card debt of young consumers. It commissions two surveys, in November 2016 and November 2020 of 2000 consumers aged 19-25 years old. These show an average credit card debt of $6,200 November 2016 with a standard deviation of $1020 compared with an average of $6,720 in October 2008 with a standard deviation of $1001. Required: a. Identify the degrees of freedom in testing for differences between the means of two independent populations where the variances in each population are unknown but assumed equal. (1 marks) b. Demonstrate the null hypothesis in testing for differences between the means of two independent populations. (1 marks) c. What is the assumption on the t test for the mean difference between two independent populations? (2 marks) d. Referring to above information, assuming that the population variances from both years are equal, is there evidence that the mean credit card debt is higher in November 2016 than in November 2020? (use the o =0.05 level of significance). (14 marks)