Explain what will happen to the firm's optimal capital structure as a result of the following changes;

a) An increase in the firm's marginal tax rate

b) an increase in the firm's investment opportunities

c) The founding owner retires from day-to-day management of the firm and hires a professional manager as his replacement

d) a decline in business risk as the industry matures

e) an increase in R&D intensity and marketing expenditures