In human engineering and product design, it is important to consider the weights of people so that airplanes or elevators aren't overloaded. Based on data from the National health Survey, the weight for adult males in the United States follows a normal distribution with a mean weight of 173 pounds and a standard deviation of 30 pounds.

a) If one U.S. adult male is randomly selected, what is the probability that his weight will be greater than 180 pounds?

b) If 36 different U.S. adult males are randomly selected, what is the probability that their sample mean weight will be greater than 180 pounds?

c) If 36 different U.S. adult males are randomly selected, what is the probability that their total weight exceeds 6480 pounds?