Assuming the bonds are trading at face value. Using the table below, what is the required rate of return on debt?

Security

Security #$1$

Security #$2$

Security #$3$

Security #$4$

$4\mathrm{.}1\%$

$3\mathrm{.}9\%$

$5\mathrm{.}9\%$

$3\mathrm{.}3\%$

Face Value

$$5,000,000$

$$6,000,000$

$$4,000,000$

$$5,000,000$

$6\%$

$4\mathrm{.}1\%$