Chemistry 2 Help?

1. The half-life of 222Rn is 3.80 days. If a sample contains 36.0 g of Rn-222, how many years will it take for the sample to be reduced to 1.00 mg of Rn-222?

Answer: 0.1597

2. A sample containing a radioactive isotope produces 2000 counts per minute in a Geiger counter. After 120 hours, the sample produces 250 counts per minute. What is the half-life of the isotope?

Answer: 40 h

Why are these the answers to the two questions. Can you please go step by step when solving it, I'm super confused. Thank you for your time.

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