A frustrated store manager is asked to make four different yes-no decisions that have no relation to

Question:

A frustrated store manager is asked to make four different yes-no decisions that have no relation to each other. Because he is impatient to leave work, he flips a coin for each decision. If the correct decision in each case was yes, what is the probability that
(a) All of his decisions were correct?
(b) None of his decisions was correct?
(c) Half of his decisions were correct?