If you get 80,000 and you have to pay 4200$ every month. How many months would it take you to pay back the loan? No interest.
***sorry, with 10% interest on loan
michael: n = LN (Pmt / (Pmt – PV x i)) / LN(1 + i)
assuming monthly compounding of interest
n = 20.83 months
Seriously? Just divide.
Divide the total owed by the amount paid every month to get the number of months of payments. Most nine-year-olds can do this. It's not a finance question, it's a third or fourth grade math problem.