A television manufacturing company performs quality assurance tests of its products before shipping them to the market. If the company chooses a random sample of 15 sets for the test, and assuming that based on previous data the company has a 6% failure rate for the newly manufactured sets, what is the probability that:

a. none of the TV sets are defective.

b. exactly one of the TV sets is defective.

c. two or fewer of the TV sets are defective.

d. three or more of the TV sets are defective.