[tex]\bf \qquad \textit{Simple Interest Earned Amount}\\\\
A=P(1+rt)\qquad
\begin{cases}
A=\textit{accumulated amount}\to &9818.75\\
P=\textit{original amount deposited}\to& \$9100\\
r=rate\to 6.41\%\to \frac{6.41}{100}\to &0.0641\\
t=years
\end{cases}
\\\\\\
\cfrac{A}{P}=1+rt\implies \cfrac{A}{P}-1=rt\implies \cfrac{\frac{A}{P}-1}{r}=t[/tex]
now, "t" is years... so if it gives you something like 3.5, that simply means, 12 + 12 + 12 + half-year or 6 months, or 42 months
