[tex]\bf ~~~~~~ \textit{Simple Interest Earned}\\\\
I = Prt\qquad
\begin{cases}
I=\textit{interest earned}\\
P=\textit{original amount deposited}\to& \$300\\
r=rate\to 3\%\to \frac{3}{100}\to &0.03\\
t=years\to &4
\end{cases}
\\\\\\ I=300\cdot 0.03\cdot 4[/tex]
the new balance is 300 + I.
