When the tree is first planted, its carbon-14 is at 100%. what has to happen for that number to start changing?

Carbon is the building block of all organic molecules and is present in many other forms in the environment, and for this to happen it is called "carbon dating" therefore i would say that it has to experience the cycle in which you can easily find looking up c 14 dating!

81 is a composite number.

answeramicable; (friendly);