Students may choose between a 3-semester-hour course in physics without labs and a 4-semester-hour course with labs. The final written examination is the same for each section. If 12 students in the section with labs made an average examination grade of 84 with a standard deviation of 4, and 18 students in the section without labs made an average grade of 66 with a standard deviation of 6, find a 99% confidence interval for the true difference between the average grades for the two courses. Can you conclude, that true average grades are significantly different