'Given that carbon-14 decays at a constant rate in such a way that it reduces to 50% in 5568 years

"Given that carbon-14
decays at a constant rate in such a way that it reduces to 50% in 5568 years,
find the age of an old wooden piece in which the carbon is only 12.5% of the
original.
`15836\\ y e a r s`
b. `16668\\ y e a r s`

c. `16704\\ y e a r s`
d. `17552\\ y e a r s`"

years