Alex, Bill, and Chen each in turn toss a balanced coin. The first one to throw a head wins.

a. What are their respective chances of winning if each tosses only one time?
b. What are their respective chances of winning if they continue, given a maximum of
two tosses each?
c. What are their respective chances of winning if they continue until someone wins?

Answers:
(a)P(A)=1/2, P(B)=1/4, P(C)=1/8
(b)P(A)=9/16, P(B)=9/32, P(C)=9/64
(c)P(A)=4/7, P(B)=2/7, P(C)=1/7

Help I don't understand how to arrive at these answers:(