To begin with, let us first write out the formula for the exponential form
[tex]y=b^{rt}[/tex]Given the initial parametrs
[tex]y=14b^t^{}[/tex]Thus
[tex]145^9=7[/tex][tex]b^{-9}=\frac{1}{2}[/tex]Using exponential laws
[tex]b=\frac{1}{(\frac{1}{2})^{\frac{1}{-\frac{1}{9}}}}[/tex]W will soon see that
[tex]b=2^{\frac{1}{9}}[/tex]Hence after 13 years, the substance left will be;
[tex]\begin{gathered} 14(2^{\frac{1}{9}})^{-13}=5.144070729 \\ \approx5.144g \end{gathered}[/tex]