A new drug is claimed to have effect on reducing heart rate for patients with unstable angina by 15 beats per minute over 24 hours. Suppose heart rate(beat per minute) of population follows a normal distribution with standard deviation 25(based on previous experience). At significance level alpha=.05, how many patients should be enrolled in the study so that the test power is guaranteed being 80% at least.
Please show the handwork, not just a statistical output.