I want an explanation for this example

Researchers want to study noise levels produced by vehicles on a busy street. The mean noise level for 29 vehicles was 82.5 decibels, with a standard deviation is 2.6 decibels.

a) Find the critical Value for the 90% confidence interval. Write exact value from the table.

b) Find the 90% confidence interval of the true mean.

Round answers to two decimal places and separate your answers with commas and no space. For example: 10.13,12.64