I hope chemistry was an okay topic, its from my earth sciences course, but didnt think that was best option. this is due tomorrow (allowed help) and i really want to understand how to do this. please help, thank you so much! :)

9. A certain radionuclide emits radiation at the rate of 15.0W at one instant of time and at 1.0W (microwatts) one hour latter. What is its half-life? (15 points)