Brain Teaser

Answer: 24 and 18 years.
The first one was sleeping 8 hours a day, so he was sleeping 1/3 of his life, so in total he was sleeping 72/3 = 24 years.
The second one was sleeping 6 hours a day, so he was sleeping 1/4 of his life, so in total he was sleeping 72/4 = 18 years.