You haven't been getting much sleep lately and want to see how you compare to the average student at your university. You plan to sample students and ask them how many hours they sleep per night. Then you will use that data to estimate the population average nightly hours of sleep with an approximate 95% confidence interval. (Critical value = 2.) Based on your own sleep, you estimate the standard deviation of hours slept to be 1.6 hours. What is the minimum number of students you need to sample in order to have a margin of error at most 0.7 hours?