The firm has $5,000 of debt on which it has to pay 10% annual interest rate (the first payment is in 1 year from now) and the firm is reducing this debt by 1% every year (i.e., in year 1, the debt will become $5, 000 0.99 etc.). The interest rate stays constant and only the interest rate payments, not principal repayments, are tax-deductible. The firm is subject to 21% corporate tax rate. Assume that every year the firm has enough profits to tax-deduct interest payments fully. What is the net present value of tax shields?