Help ? probability question? thank you

A hospital has two rooms for surgery. The probability that a given room is free
is 0.5. Show your work in answering the following questions:
(a) What is the probability that both rooms are free?
(b) What is the probability that both rooms are occupied? { would the answer be zero}
(c) What is the probability that at least one room is free? {would this be .5}

P(room free) = 0.5, P(room occupied) = 1 - 0.5 = 0.5
use the multiplicative principle

a. 0.5*0.5 = 0.25 <-------

b. 0.5*0.5*0.25 <-------

c. 1 - (0.25 + 0.25) = 0.5 <-------