With a height of 69 ​in, Ronald was the shortest president of a particular club in the past century. The club presidents of the past century have a mean height of 73.7 in and a standard deviation of 2.6 in. a. What is the positive difference between Ronald​'s height and the​ mean? b. How many standard deviations is that​ [the difference found in part​ (a)]? c. Convert Ronald​'s height to a z score. d. If we consider​ "usual" heights to be those that convert to z scores between minus2 and​ 2, is Ronald​'s height usual or​ unusual?