The Office of Student Services at a large western state university maintains information on the study habits of its full-time students. Their studies indicate that the mean amount of time undergraduate students study per week is 20 hours. The hours studied follows the normal distribution with a population standard deviation of 7 hours. Suppose we select a random sample of 105 current students. What is the standard error of the mean of this sample is between 19.25 hours and 21.0 hours?