If you know the population standard deviation (sigma σ) known, use the z-distribution. If you do not know sigma, use the t-distribution.

Enter your data in the blue cells. All the yellow answer cells will be updated accordingly.

Note:  If you are given the population size, N, enter it in the appropriate cell and check to see if the Finite Population Correction Factor is needed. Use either the Larson (233) or McClave (503) answer as needed. If you are not given the population size, the FPCF is not needed and the Population Size N cell does not matter to your answer.
Hope this helps.
Dr. Dawn