Can anyone help me Find the critical value that should be used in constructing the confidence interval?

A survey of several 11 to12 year olds recorded the following amounts spent on a trip to the mall:

$18.35, $25.19, $27.45

Construct the 80% confidence interval for the average amount spent by 11 to 12-year olds on a trip to the mall. Assume the population is approximately normal.

Rounded to three decimal places