Answer
$t = 2.97 \times 10^9 y$
Work Step by Step
From the radioactive dating equation,
$N_U = N_{Uo}e^{-\lambda t} $
Solve for t.
$t = -\frac{1}{\lambda} ln \frac{N_U}{N_{Uo}}$
$t = - \frac{4.47 \times 10^{9}} {ln2 } ln [\frac{1.06 \times 10^{19}}{1.684 \times 10^{19}}]$
$t = 2.97 \times 10^9 y$
