Independent flips of a coin that lands on heads with probability $p$ are made. What is the probability that the first four outcomes are
(a) $H, H, H, H ?$
(b) $T, H, H, H ?$
(c) What is the probability that the pattern $T, H, H, H$ occurs before the pattern $H, H, H, H ?$
Hint for part $(c):$ How can the pattern $H, H, H, H$ occur first?