please help this probability and statistics questions

(a) During the early summer break arrangement in Hong Kong, a large number of teachers have arranged additional online classes to their students. A reporter contacted a random sample of 36 secondary school students. He found that these students spent a mean of 4.1 hours per week on additional classes. Assume that the time spent on additional classes during the early summer break arrangement for all secondary school students in Hong Kong are normally distributed with a population standard deviation of0.4 hour. (i) Find the best point estimate for the true mean time spent on additional classes. Correct your answer to 1 decimal place. (I mark) (ii) Determine the sample size required to produce a 98.6% condence interval for the true mean time spent on additional classes with a margin of error of 0.1 hour. (3 marks) (iii) Find a 90.?% condence interval for the true mean time spent on additional classes. Correct your answers to 2 decimal places. (4 marks)