The correct answer is: $0.3181818\ldots$ (i.e. $0.3\overline{18}$).
Explanation
Let $x=0.3181818\ldots$. Then
$$100x=31.8181818\ldots$$
Subtract:
$$100x-x=31.8181818\ldots-0.3181818\ldots$$
$$99x=31.5$$
$$x=\frac{31.5}{99}=\frac{315}{990}=\frac{7}{22}.$$
Note: the repeating block is “18” (after the initial 3). The form $0.\overline{318}$ is different (it equals $106/333$), so it is not equal to $7/22$.