the radioactive element carbon -14 has a half life of 5750 years. a scientist determined that the bones from a mastodon had lost 52.5% of their carbon-14 . how old were the bones at the time they were discovered

Sanya noticed that the temperature was falling at a steady rate of 1.4 degrees every hour from the time that she first checked her outdoor thermometer. by 6 a.m., the temperature had fallen 21 degrees. which expression can you use to find how many hours earlier she had first checked the thermometer?