Use the half life to determine k.
k = 0.693/t(1/2).
Then use
ln(No/N)=kt
No = the number of atoms you started with. Since that isn't given, just assume as easy number like 100. Then N is what you have now which the problem lists as 6.3% of the number you started with. You know k, and that leaves t (time) as the only unknown.
A skull fragment found in 1936 at Baldwin Hills, California, was dated by 14C analysis. Approximately 100g of bone was cleaned and treated with 1 M HCl(aq) to destroy the mineral content of the bone. The bone protein was then collected, dried and pyrolyzed. The CO2 produced was collected and purified, and the ratio of 14C to 12C was measured. If the sample contained roughly 6.3 % of the 14C present in living tissue, how old was the skeleton? (For 14C, T1/2 = 5.73 × 103 years.)
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