Tp = 12.33 yr

l p = 0.693/12.33 = 0.0562 yr-1
 

410 = 670 e-leff2

-0.4911 = -leff(2)

leff = 0.2456 yr-1

leff = lx + lp

lx = 0.2456 - 0.0562 = 0.1894 yr-1

Tx = 0.693/0.1894 = 3.7 yr

Answer is D

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