Krypton-79 has a half-life of 35 hours. how many half-lives have passed after 105 hours?

The number of half - lives that has passed after 105 hours for krypton-79 that has half-life of 35 hours is calculated as below

if 1 half life = 35 hours

what about 105 hours = ? half-lives

= (1 half life x105 hours) / 35 hours = 3 half-lives has passed after 105 hours