Carbon-14 Dating Calculation

A linen scroll contains 80.9% of Carbon-14 that it contain when new. How old are the scrolls if the half-life for deacy is 5.73X10^3?
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ln(M/Mo) = -kt
n = natural log
M = mass left (not needed)
Mo = original mass (not needed)
(M/Mo) = 0.809
k = 0.693/T(half)
T(half) = 5.73x10^3 years.
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