Carbon-14 Dating Age Calculation

[xinlan]

Homework Statement

Find the age t of a sample, if the total mass of carbon in the sample is m_c, the activity of the sample is A, the current ratio of carbon 14 to total carbon in the atmosphere is r , and the decay constant of carbon 14 is lamda . Assume that, at any time, carbon 14 is a negligible fraction of the total mass of carbon and that the measured activity of the sample is purely due to carbon 14 . Also assume that the ratio of carbon 14 to total carbon in the atmosphere (the source of the carbon in the sample) is the same at present and on the day when the number of carbon 14 atoms in the sample was set.
Express your answer in terms of the mass m_a of a carbon 14 atom, m_c ,A , r , and lamda.

Homework Equations

t = Ln(N) / Ln(No)* -lamda

The Attempt at a Solution

t = Ln(N) / Ln(No)* -lamda
t = Ln(R) / Ln(Ro)* -lamda
= Ln(A) / Ln (r)* -lamda

but then I don't know how to corporate with other terms..
please help me.. thanks..

 

[xinlan]

please somebody help me.. this is urgent..