To histroically date objects less than 50,000 years old, carbon 14 dating is used. Carbon 14 has a half life of 5730 years. Before death animals and vegetation have a reading for carbon 14 of 12.5 counts per minute on a Geiger counter. Show that the decay rate of carbon 14 is -1.21 *10^(-4). If a piece of wood from an excavation site has a reading of 7 counts per minute, show that the wood's age is approximately 4800 years.
I did the first part anf ound the rate.
The second part, I don't even know where to start. What does it mean?