Obliczanie przedziału t dla średniej

An economist studying fuel costs wants to estimate the mean price of gasoline in her state on a certain day. On that day, she takes an of $12$12 gas stations and finds the sample mean price (in dollars per gallon) is $\bar x=\$2.29$x, with, \bar, on top, equals, dollar sign, 2, point, 29 with a standard deviation of $s_x=\$0.20$s, start subscript, x, end subscript, equals, dollar sign, 0, point, 20. The prices in the sample are roughly symmetric with no distinct outliers.