Given:
First payment = $800 due today
Second payment = $600 in 9 months
Interest rate = 10.5% compounded monthly
The interest is to be settled in a payment of $800 in 6 months and a final payment in 24 months.
Let's determine the final payment if the money is now worth 9.5% compounded quarterly.
Apply the compound interest formula:
![A=P(1+(r)/(n))^(nt)](https://img.qammunity.org/2023/formulas/mathematics/high-school/39foo2gerf9tf1ffk32zwshrn339mz02kv.png)
Let x represent the initial amount of debt.
Thus, we have the equation:
![\begin{gathered} (x-800)(1+(0.105)/(12))^{12\ast(9)/(12)}=600 \\ \\ (x-800)(1.00875)^9=600 \\ \\ (x-800)(1.08156)=600 \\ \\ x-800=(600)/(1.08156) \\ \\ x=1340.44 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/uxsy3zuc97jz4rxvs3sweqj92z9jjoozu7.png)
For the amount due in six months, we have:
![\begin{gathered} A=1340.44(1+(0.095)/(4))^{4\ast(6)/(12)}_{} \\ \\ A=1340.44(1.02375)^2 \\ \\ A=1404.87 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/hwnrgbsdzz02pdepsx04vt3f9zeqfgt1gp.png)
Hence, the amount which is due after 6 months will be:
$1404.87 - $800 = $604.87
Now, let's find the payment due in 24 months.
Number of months remaining = 24 - 6 = 18 months.
Hence, we have:
![\begin{gathered} A=604.87(1+(0.095)/(4))^{4\ast(18)/(12)} \\ \\ A=604.87(1.02375)^6 \\ \\ A=696.35 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/una124b3c6ulphwwe44spcx1ys7ayburfu.png)
Therefore, the final payment if the money is now worth 9.5% compounded quarterly is $696.35
ANSWER:
$696.35