Distinguish the difference between point estimate as well as confidence interval, at the 95% confidence level. A company producing electrical liquid mosquito-repellent intends to determine its product's lifetime. Suggest the following situations:

(a) Assume that the lifetime of product follows a normal distribution with population standard deviation of 9 hours. If 9 products are taken randomly as samples, then sample mean would be 100 hours.

(b) Assume that the lifetime of product follows a normal distribution with unknown standard deviation. If 9 products are taken randomly as sample, then sample mean would be 100 hours with sample standard deviation of 10 hours.

(c) Assume that the distribution of lifetime of product is unknown, but the populition standard deviation is know to be 9 hours. If 9 products are taken randomly as samples, then sample mean would be 100 hours.