Simple question about loan in "The Book On Real Estate Investing"

[Eddie Wu]

Hello BiggerPockets community! I am new to REI and am just recently starting to read the book The Book On Rental Property Investing by Brandon Turner, and I have a question about the loan calculation in first part of this chapter, where it talks about How to Make $1,000,000 Through Rental Properties. This question may seem very simple for you folks, but I am hoping to get some explanations here if possible. 

My questions are about the content from page 53-55. For simplicity, I will rephrase the problems here:

We purchase a fourplex in the beginning of our first year for $80,000, where $16,000 are used as down payment, $4,000 are used on minor repairs and improvements to satisfy the standard 10% appreciation in the first year, and we are borrowing $64,000 from the bank. Each unit nets $200 per month after all expenses have been paid. 

After first year, the loan is said to be $63,500 approximately (My first question is why it is $63,500 but not $64,000), and cash flow saved is ~$10,000 (technically $9,600). 

After second year, the loan becomes $63,000 approximately (My second question is to confirm does this mean that annual payment of the loan is $500), and the cash flow saved is $20,000. 

At the start of year three, a second fourplex is purchased with the same numbers (same price, same cash flow) using cash flow saved from the first two years, $20,000 (same as before $16,000 is used for purchase and $4,000 is used for forced appreciation). 

At the end of year three, the combined loan becomes $126,000 (I assume it's the addition of $63,500 and $62,500, where the former is the new loan and the second one is the older loan after paying out $1,000. Please correct me if I miss anything here), and the annual combined cash flow saved is now $20,000. 

At the end of year four, it is said in the book that we "rinse and repeat" once again by purchasing a third fourplex with the same numbers, and the totals for the end of year four are combined loans of $177,000 (This is my biggest question. I have no idea where this number comes from. If $20,000 from saved cash flow is used to purchase the house + forced appreciation, then like before the new loan should be $63,500, but when we add this amount with the previous combined loans, in this case it is $124,000 as $2,000 has been paid out since the beginning of year three with $500 per year for each of the two outstanding loans, assuming interest rate stays roughly the same, and $124,000 + $63,500 should actually be closer to $187,500 than the $177,000 used in the book). 

I know it is a lot of words I have used to describe the problem, but if anyone can help or know more about the calculation here, please explain the logics as it's been bugging me during my read. Thanks for any advice!