Calculation:

Converting \(\displaystyle{1.5}\%\) monthly to yearly.

\(\displaystyle{i}={\frac{{{x}}}{{{12}}}}\) .........(I)

Here the interest rate annually is x and the interest rate monthly is i.

Substitute \(\displaystyle{1.5}\%\) for i in Equation (I).

\(\displaystyle{1.5}\%={\frac{{{x}}}{{{12}}}}\)

\(\displaystyle{x}={18}\%\)

Hence \(\displaystyle{1.5}\%\) monthly interest rate is closest to \(\displaystyle{18}\%\) yearly.

Conclusion:

Thus, the correct option is (b) \(\displaystyle{18}\%\) effective interest per year.

Converting \(\displaystyle{1.5}\%\) monthly to yearly.

\(\displaystyle{i}={\frac{{{x}}}{{{12}}}}\) .........(I)

Here the interest rate annually is x and the interest rate monthly is i.

Substitute \(\displaystyle{1.5}\%\) for i in Equation (I).

\(\displaystyle{1.5}\%={\frac{{{x}}}{{{12}}}}\)

\(\displaystyle{x}={18}\%\)

Hence \(\displaystyle{1.5}\%\) monthly interest rate is closest to \(\displaystyle{18}\%\) yearly.

Conclusion:

Thus, the correct option is (b) \(\displaystyle{18}\%\) effective interest per year.