A study is being conducted to study the effect that a calcium-channel-blocking agent has on heart rate in patients with unstable angina. We need to estimate the sample size required to detect a change in the mean heart rate by 5 beats per minute in either direction. Assume the hypothesis test being performed is two-sided with a significance level of = 0.05, estimated standard deviation of 12, and 80% power. What sample size is required? Remember that when calculating the sample size, you must round up to the nearest whole number