A sample of 20 small bags of the same brand of candies was selected. Assume that the population distribution of bag weights is normal. The weight of each bag was then recorded. The mean weight was 3 ounces with a standard deviation of 0.13 ounces. The population standard deviation is known to be 0.1 ounce.

Construct a 90% confidence interval for the population average weight of the candies. with error bound

along with 98% and error bound.
I am finding this part super confusing. Can someone please explain how to get my answers?

Question

A sample of 20 small bags of the same brand of candies was selected. Assume that the population distribution of bag weights is normal. The weight of each bag was then recorded. The mean weight was 3 ounces with a standard deviation of 0.13 ounces. The population standard deviation is known to be 0.1 ounce.

Construct a 90% confidence interval for the population average weight of the candies. with error bound 

along with 98% and error bound.
I am finding this part super confusing. Can someone please explain how to get my answers?