Mega Corp. has $500 million in 10-year bonds with an interest rate of 6.5% outstanding as well as $300 million in 5-year bank loans with an interest rate of 5.25%. Its effective corporate tax rate is 23%. What is its average after-tax interest rate expense? a $ 1.4% b 4.6% c 4.5 % d 4.2% e 6.0%