The ratio of the number of atoms of two radioactive elements $\mathrm{A}$ and $\mathrm{B}$, in equilibrium with each other, is $3.1\times {10}^9:1$. If ${\mathrm{t}}_{\frac{1}{2}}$ of element $\mathrm{B}$ is $6.45$ years, calculate ${\mathrm{t}}_{1/2} (\mathrm{Half}-\mathrm{life})$ of element $\mathrm{A}$.

Give your answer up to one decimal place and if the answer is $\mathrm{X}\times {10}^{\mathrm{y}}, \text{give the value of X.}$