A simple random sample of the weights of 40 women has mean of 146.22 lb. Reasearch from other sources suggests that the population standard deviation of weight of women is 30.86lb. Find a 95% confidence interval estimate of the mean weight of all women.
I know the answer is 136.66 lb<u<155.78lb but I just need a step by step explaination on why this is the answer! I'd be greatly appreciated <3