Please solve it

An investor is considering opening up a new restaurant in the city of Baku, but doesn't know what type of restaurant is in demand. A study is run to learn about the spending habits of people in Baku who go out for dinner. A random sample of 25 people were selected, and asked the cost of the last time they went out for dinner. The results from the survey had a sample mean of)? = 65 manats and a sample standard deviation of 5 = 25 manats. Assume the amount of money spent is normally distributed. a. [3] Find a 90% confidence interval for the mean cost of a dinner in Baku. b. [3] The investor plans to run a larger survey. Assuming that the true (population) standard deviation is known to be a = 25, what is the minimum sample size such that we are able to estimate the true mean within a 5 margin of error, 95% of the time