[tex]\bf \qquad \qquad \textit{Future Value of an ordinary annuity}
\\\\
A=pymnt\left[ \cfrac{\left( 1+\frac{r}{n} \right)^{nt}-1}{\frac{r}{n}} \right][/tex]
[tex]\bf \begin{cases}
A=
\begin{array}{llll}
\textit{original amount}\\
\textit{already compounded}
\end{array} &
\begin{array}{llll}
\end{array}\\
pymnt=\textit{periodic payments}\to &
\begin{array}{llll}
485\cdot 12\\
\underline{5280}
\end{array}\\
r=rate\to 6\%\to \frac{6}{100}\to &0.06\\
n=
\begin{array}{llll}
\textit{times it compounds per year}\\
\textit{a year, thus once}
\end{array}\to &1\\
t=years\to &4
\end{cases}
\\\\\\
[/tex]
[tex]\bf A=5280\left[ \cfrac{\left( 1+\frac{0.06}{1} \right)^{1\cdot 4}-1}{\frac{0.06}{1}} \right][/tex]
Joe is making $485 payments monthly, but the amount gets interest on a yearly basis, not monthly, so the amount that yields interest is 485*12
also, keep in mind, we're assuming is compound interest, as opposed to simple interest
