In a random sample of 80 students in first grade the main hours of sleep per night was 9.4 with a standard deviation of 0.41 in a random sample of 50 students in 12th grade the main hour of sleep per night was 7.5 with a standard deviation of 0.52. which interval is a 99% code finance interval for the difference between the main hours of sleep.
(1.75 h, 2.05 h)
(1.89 h, 1.91h)
(1.43 h, 2.37h)
(1.68 h, 2.12 h)