A)
[tex]\bf \qquad \qquad \textit{Future Value of an ordinary annuity}\\
\left. \qquad \qquad \right.(\textit{payments at the end of the period})
\\\\
A=pymnt\left[ \cfrac{\left( 1+\frac{r}{n} \right)^{nt}-1}{\frac{r}{n}} \right][/tex]
[tex]\bf \qquad
\begin{cases}
A=
\begin{array}{llll}
\textit{accumulated amount}\\
\end{array}\begin{array}{llll}\end{array}\\
pymnt=\textit{periodic payments}\to &25000\\
r=rate\to 11.5\%\to \frac{11.5}{100}\to &0.115\\
n=
\begin{array}{llll}
\textit{times it compounds per year}\\
\textit{quarterly, four times}
\end{array}\to &4\\
t=years\to &15
\end{cases}
\\\\\\
A=25000\left[ \cfrac{\left( 1+\frac{0.115}{4} \right)^{4\cdot 15}-1}{\frac{0.115}{4}} \right][/tex]
B)
well, the company is depositing 25,000 every three months, thus it does that 4 times per year, that means yearly they're putting out of their pocket 100,000, for 15 years, that means 1,500,000.
what's the interest earned? well, the amount you've got from A minus 1,500,000, or A - 1,500,000, the difference is what came from the yield.
