Science Homework Help

1. The half-life of cobalt-60 is 5.27 years. How many milligrams of cobalt-60 remain after 52.7 years if you start with 15 mg?
2. A sample contains 12.0 mg of an unknown element. After 4.46 × 109
   years, the sample will contain 3.00 mg of the unknown element. What is
   the half-life of the unknown element?

Please show the work for each question.