Fred, Wilma, Betty, and Barney have all been invited to Mr. Slate's birthday party. They arrive randomly and at different ×. In how many ways can they arrive? In how many ways can Wilma arrive first and Fred last? Find the probability that Wilma will arrive first and Fred will arrive last.
a. 24; 6; 1/24
b. 24; 3; 1/12
c. 24; 2; 1/48
d. 24; 1; 1/24