How much of a 100 gram sample of isotope remain unchanged after two hours?

To determine how much of a 100-gram sample of an isotope remains unchanged after two hours, we need to know its half-life. For example, if the half-life is one hour, after two hours, two half-lives would have passed, resulting in 25 grams remaining (100g → 50g after one hour, then 50g → 25g after another hour). If the half-life is different, the remaining amount would be calculated accordingly. Please specify the half-life for a precise answer.