$${T_{1/2} = \frac{(2,560 \times 10^{20}) \ln 2}{4490\, \mathrm{s^{-1}}} \\ = 3,95 \times 10^{16}\, \mathrm{s} = \underline{\underline{1,25 \times 10^9\, \mathrm{a}}}}$$