The half-life exponential decay equation is
[tex]\begin{gathered} N(t)=N_0(\frac{1}{2})^{\lambda} \\ \text{where} \\ \lambda=\frac{t}{t_{\frac{1}{2}}} \end{gathered}[/tex]N_0 is the initial quantity of the substance, t_1/2 is the half-life and t is the time.
In our case,
[tex]\begin{gathered} \lambda=\frac{300}{710}=\frac{30}{71} \\ N_0=30 \end{gathered}[/tex]Therefore,
[tex]N(300)=\frac{30}{2^{\frac{30}{71}}}=22.3833\ldots\approx22.383_{}[/tex]The answer is 22.383 grams.