We known that $N =N_{0} \times\left(\frac{1}{2}\right)^{2}$
Here, $N=\frac{1}{16}, N_{0}=1$, by putting the values
$\frac{1}{16}=1 \times\left(\frac{1}{2}\right)^{n} \,\,\therefore n =4$
We know that $T=t_{1 / 2} \times n$$\therefore T=1580 \times 4=6320$ years