4.39 A company installs new central-heating furnaces and has found that for 15% of all installations, a return visit is needed to make some modifications. Six installations were made in a particular week. Assume independence of outcomes for these installations.

a. What is the probability that a return visit will be needed in all these cases?

b. What is the probability that a return visit will be needed in none of these cases?

c. What is the probability that a return visit will be needed in more than 1 of these cases?