Answer:
c. $50,000
Explanation:
Dr Cash 500,000
  Cr Common stock 100,000
  Cr Additional paid in capital 400,000
Dr Treasury stock 100,000
  Cr Cash 100,000
Dr Cash 80,000
  Cr Treasury stock 50,000
  Cr Additional paid in capital 30,000
Treasury stock's balance = $100,000 - $50,000 = $50,000 debit