If an object has 6.25% of the C-14 activity as a living organism, the age of the item is: ?

Question

If an object has 6.25% of the C-14 activity as a living organism, the age of the item is: ?

Answer 1

The half-life of C-14 is 5,700 years, so at that time only 50% of the C-14 will still be there.

After another 5,700 years, another half will be gone, leaving 25% of the C-14.

Another 5,700 years, and 12.5% is left.

Another 5,700 years, and 6.25% is left.

Add those together, and the total age is 22,800 years.