Answer
$P = \frac{A~(\frac{r}{n})}{~(1+\frac{r}{n})^{nt}~-1}$
The resulting formula describes the amount of the periodic deposit $P$ required in an annuity.
Work Step by Step
$A = \frac{P~[(1+\frac{r}{n})^{nt}~-1]}{(\frac{r}{n})}$
$P = \frac{A~(\frac{r}{n})}{~(1+\frac{r}{n})^{nt}~-1}$
The resulting formula describes the amount of the periodic deposit $P$ required in an annuity if we want to end up with a final amount, $A$, with an interest rate of $r$ compounded $n$ times per year for a time of $t$ years.
