Boron has two stable isotope, $_5 B^{11}$ and $_5 B^{11}$ Their respective masses are $10.01294 \;amu$ and $11.00931\;amu$ and the atomic weight of Boron in $10.811\;amu$ . Find the abundances of $_5B^{ 10}$ and $_5B^{11}$

Question

$\begin{array}{1 1} _5B^{10}=19.9 \% \;and \;_5B^{10} =80.1 \% \\ _5B^{10}=80.1 \% \;and \;_5B^{11} =19.9 \% \\ _5B^{10}=75 \% \;and \;_5B^{11} =25 \% \\ _5B^{10}=25 \% \;and \;_5B^{11} =75 \% \end{array} $