Chemistry question, homework help

In this lesson, you learned about calculating with half-life. Now, you will demonstrate your understanding of half-life by answering the following questions.Make sure that you are showing each step of your work.

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?