[tex]\bf ~~~~~~~~~~~~\textit{Future Value of an ordinary annuity}\\
~~~~~~~~~~~~(\textit{payments at the end of the period})
\\\\
A=pymnt\left[ \cfrac{\left( 1+\frac{r}{n} \right)^{nt}-1}{\frac{r}{n}} \right] \\\\\\
~~~~~~
\begin{cases}
A=\textit{accumulated amount}\\
pymnt=\textit{periodic payments}\to &3350\\
r=rate\to 19.7\%\to \frac{19.7}{100}\to &0.197\\
n=
\begin{array}{llll}
\textit{times it compounds per year}\\
\textit{annually, thus once}
\end{array}\to &1\\
t=years\to &7
\end{cases}[/tex]
[tex]\bf A=3350\left[ \cfrac{\left( 1+\frac{0.197}{1} \right)^{1\cdot 7}-1}{\frac{0.197}{1}} \right]\implies A=3350\left[\cfrac{1.197^7-1}{0.197} \right]
\\\\\\
A\approx 3350(12.7966673797946)\implies A\approx 42868.8357223119[/tex]
now, for 7 years she has been depositing $3350, so the amount that she put out of her pocket is 7*3350.
and we know the compounded amount is A, so the interest is just their difference.
42868.8357223119 - (7 * 3350).
