For each of the following, indicate if the number of half-lives elapsed is:

1. one half-life
2. two half-lives
3. three half-lives

a. a sample of Ce-141 with a half-life of 32.5 days after 32.5 days
b. a sample of F-18 with a half-life of 110 min after 330 min
c. a sample of Au-198 with a half-life of 2.7 days after 5.4 days