An unlevered firm adds debt to its capital structure. The interest rate on the firm's

debt is $10\%.$ Its unlevered cost of equity is $14\%.$ The marginal tax rate is $35\%.$ The

firm starts with a capital structure of $10\%$ debt and $90\%$ equity in year $1,$ where the

debt level is $$10$ million. The firm increases its debt level by $$5$ million per year in

year $2$ and year $3,$ but then debt remains constant at $$20$ million beyond year $3.$

What is the present value of the interest tax shield?

a$)$ $$6\mathrm{.}54$ million

b$)$ $$5\mathrm{.}23$ million

c$)$ $$7\mathrm{.}57$ million

d$)$ $$4\mathrm{.}70$ million