Answer:
4 millions
Step-by-step explanation:
First, we will check how much was amortizate for the first loan:
Principal 100 million
on 10 equal payment
amortization per year 100/10 = 10 millions
we refinance at the end of the fourth installment
10 x 4 = 40 millions
The principal at the end of year four:
Principal 100 millions - 40 millions = 60 millions
This amount will be paid on 15 years with 15 equal payment
60 million / 15 years = 4 millions