The Speeds of 180 Randomly Chosen Cars Passing a Certain $104.2 \mathrm{~km} / \mathrm{h}$

The speeds of 180 randomly chosen cars passing a certain point on a highway were measured. The mean was found to be $104.2 \mathrm{~km} / \mathrm{h}$ and their standard deviation was $6.1 \mathrm{~km} / \mathrm{h}$ . Estimate the mean speed of the entire population of cars with a confidence level of $95 \%$ .