Question 3. A Lego retailer has a concern about his store sales in last year. To test his concern, he decided to conduct statistical inference on the average daily sales and the variance of daily sales in last year. As a start, he is interested in constructed in confidence interval. By assuming the distribution of daily sales follows a normal distribution, he randomly selected 61 daily sales number. a) (2 marks) If the population standard deviation is 4, and the sample mean is 10. Find the 90% confidence interval (show your final answer correct to two decimal places). b) (2 marks) If, instead, we only know the sample standard deviation which equals 4, and given the higher end of a 95% confidence interval which equals 2.5, find the observed sample mean (show your final answer correct to two decimal places). c) (6 marks) Given the significance level B = 0.01. and the sample standard deviation s = 3.8. Perform a hypothesis testing (with detailed steps) to test g?> 4