4. A high school principal studied the amount of time her students devote to working at an after-school job. She randomly selected 15 students, obtained their working hours, and computed the sample mean to be 12.3 hours and the sample standard deviation of 11.2 hours. If her school is a representative sample of the state, find a 90% confidence interval estimate of the average amount of time (µ) the students work at an after school job in her state.