#### Answer

$6.168 \%$

#### Work Step by Step

Recall:
Effective Rate of Interest Formula
$$r_e = \left(1+\dfrac{r}{n} \right)^n - 1$$
where
$r_e:$ Effective Rate of Interest
$r:$ Annual Interest Rate
$n:$ Number of compoundings per year
The given problem has:
$r = 0.06$
$\text{Compounded monthly} \to n = 12$
Thus, using these valules and the formula above gives:
$r_e = \left(1+\dfrac{0.06}{12} \right)^{12} - 1$
$r_e \approx 0.06168$
$r_e \approx 6.168 \%$