A salesman normally makes a sale $($closes$)$ on $75\%$ of his presentations. Assuming the presentations are independent,

find the probability of each of the following.

a$)$ He fails to close for the first time on his fifth attempt.

b$)$ He closes his first presentation on his fourth attempt.

c$)$ The first presentation he closes will be on his second attempt.

d$)$ The first presentation he closes will be on one of his first three attempts.