4. A taxi company is trying to decide whether to purchase brand A or brand B tires for its fleet of taxis. To estimate the difference in the two brands, an experiment was conducted using 12 of each brand. The results are as follows: Brand A: x1 = 36300 km, S1 = 5000 km Brand B: X2 = 38100 km, S2 = 6100 km (a) Test if the two population variances can be treated to be equal. Use a = 0.05 and the critical value method. [5 marks (b) Can you conclude if the two population means are equal at 5% level of significance? Use the critical value method. [6 marks]