Ying Import has several bond issues outstanding, each making semiannual interest payments. The bonds are listed in the following table. If the corporate tax rate is 31 percent, what is the aftertax cost of Ying's debt (leave your answer as an APR)? (Do not round your intermediate calculations.)

Bond	Coupon Rate	Yield to Maturity	Price Quote (% of Face Value)	Maturity	Face Value
1	6.30%	6.30%	100	6 years	$ 17,000,000
2	7.40%	6.09%	109	9 years	$ 37,000,000
3	6.70%	6.61%	101	21 years	$ 42,000,000
4	7.50%	6.53%	113	32 years	$ 55,000,000

a. 4.65%

b. 6.42%

c. 4.21%

d. 4.43%

e. 4.25%