Which statements are true regarding nuclear stability?

In the decay sequence:

${}_{92}{}^{238}\mathrm{U}\stackrel{-{\mathrm{x}}_1}{\to }{}_{90}{}^{234}\mathrm{Th}\stackrel{-{\mathrm{x}}_2}{\to }{}_{91}{}^{234}\mathrm{Pa}\stackrel{-{\mathrm{x}}_3}{\to }{}_{\mathrm{ }}{}^{234}\mathrm{Z}\stackrel{-{\mathrm{x}}_4}{\to }{}_{90}{}^{234}\mathrm{Th}$

${\mathrm{x}}_1,\mathrm{ }{\mathrm{x}}_2,\mathrm{ }{\mathrm{x}}_3$ and ${\mathrm{x}}_4$ are the particles/ radiation emitted by the respective isotopes. The correct option(s) is/are:

In a sample of pitchblende, the atomic ratio is ${}^{206}\mathrm{Pb}:{}^{238}\mathrm{U}=0.23:1.$The age of the mineral is $\mathrm{B} \times {10}^9$, if the half-life of uranium is taken as $4.5\times {10}^9$ years. All lead originated from uranium. (Report the value of B in two significant figures.)

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 $\mathrm{X}\times {10}^{\mathrm{y}}, \text{give the value of X.}$