Answer:

Explanation:
For this case the total payment is $320000, and she pays $40000 so the remain amount to pay would be:
$320000-40000=$ 280000
For this case we assume that the annual interest rate is APR=5.7% =0.057 on fraction.
The total number of years are 20. For this case n represent the number of payments per year and since we have monthly payments then n =12.
In order to find the PMT we can use the following formula:
![PMT= \frac{P(\frac{APR}{n})}{[1-(1+\frac{APR}{n})^{-nt}]}](https://tex.z-dn.net/?f=%20PMT%3D%20%5Cfrac%7BP%28%5Cfrac%7BAPR%7D%7Bn%7D%29%7D%7B%5B1-%281%2B%5Cfrac%7BAPR%7D%7Bn%7D%29%5E%7B-nt%7D%5D%7D)
On the last expression the APR needs to be on fraction and P represent the principal amount, for this case P = $280000. So if we replace we got:
![PMT= \frac{280000(\frac{0.057}{12})}{[1-(1+\frac{0.057}{12})^{-12*20}]}](https://tex.z-dn.net/?f=%20PMT%3D%20%5Cfrac%7B280000%28%5Cfrac%7B0.057%7D%7B12%7D%29%7D%7B%5B1-%281%2B%5Cfrac%7B0.057%7D%7B12%7D%29%5E%7B-12%2A20%7D%5D%7D)

And we can verify this using the following excel function: "=PMT(0.057/12,12*20,-280000)"