[tex]\bf \qquad \textit{Simple Interest Earned}\\\\
I = Prt\qquad
\begin{cases}
I=\textit{interest earned}\\
P=\textit{original amount deposited}\to& \$690.65\\
r=rate\to 7.3\%\to \frac{7.3}{100}\to &0.073\\
t=years\to &\frac{15+31+30+6}{365}
\end{cases}[/tex]
the penalty he'll incurred into, since July 6 is after the deadline of April 15, is I = Prt
now "t" is in years, how many days after April 15 to July 6? well, 15 + 31 + 30 +6, to convert to years, divide by 365