Answer
a) is the correct answer.
Work Step by Step
$rate = k[A] = (0.018 s^{-1})(0.50M) = 0.009 M/s$
If you calculate k as:
$$k = \frac{2.2 \times 10^{-3} M/s}{0.12 \ M} $$ as in 14.2.2, in order to get a more accurate result.
$rate = k[A] = (\frac{2.2 \times 10^{-3} M/s}{0.12 \ M} )(0.50M) = 0.0092 M/s$
