Answer:
$50,000
Step-by-step explanation:
The initial balance of Dr. Kim's student loan debt was $200,000 and it was completely repaid after working for 4 years, therefore, Dr. Kim must report annual income of $200,000 / 4 = $50,000 during each of the 4 years that he worked on an Indian reservation. He didn't actually receive any money, but since his liabilities decrease, he must report it as income.