keeping in mind that 9 months is not even a year, since there are 12 months in a year, then 9 months are 9/12 year, or 3/4 of a year.
[tex]\bf \qquad \textit{Simple Interest Earned Amount}\\\\
A=P(1+rt)\qquad
\begin{cases}
A=\textit{accumulated amount}\\
P=\textit{original amount deposited}\to& \$300\\
r=rate\to 2.5\%\to \frac{2.5}{100}\to &0.025\\
t=years\to \frac{9}{12}\to &\frac{3}{4}
\end{cases}
\\\\\\
A=300\left( 1+0.025\cdot \frac{3}{4} \right)[/tex]
