Can someone help with this:

The average commute times for employees of a large company is 27 minutes. The commute time of 12 employees are 31, 10, 13, 42, 20, 23, 23, 27, 25, 31, 18, and 13.
Determine the sample mean and the population mean.
What is the estimated margin of error of the sample population, using standard deviation?