What is the effect of a larger sample size on the interval estimate ...

A simple random of 60 items resulted in a sample mean of 80. The population standard deviation is standard deviation=15
a) compute the 95% confidence for the population mean.
b) Assume that the same sample mean was obtained from a sample of 120 items. Provide a 95% confidence interval for the population mean.
c) What is the effect of a larger sample size on the interval estimate?