A firm recently issued $1,000 par value, 20-year bonds with a coupon rate of 6% and semi-annual payments. The bonds sold at par value, but flotation costs amounted to 5% of par value. The firm has a marginal tax rate of 21%. What is the firm's cost of debt for these bonds?
a) 5.09%
b) 6.00%
c) 4.74%
d) 9.48%
e) 6.45%