Please show calculations.

Wilde Software Development has a 12% unlevered cost of equity. Wilde forecasts the following interest expenses, which are expected to grow at a constant 4% rate after Year 3. Wilde's tax rate is 25%.

Interest expenses:

Year 1: $80

Year 2: $100

Year 3: $120

(a) What is the horizon value of the interest tax shield? (Note: according to the book's appendix, the answer is $390)

(b) What is the total value of the interest tax shield at Year 0? (Note: according to the book's appendix, the answer is $336.7347)