The value of $x$ is $18$, and its deviation from the mean is $3$.

The sum of the deviations of all five values from the mean is $0$, i.e., $\sum_{i=1}^{5} (x_i - \bar{x}) = 0$.

The value of $x$ is $12$, and its deviation from the mean is $-3$.

The sum of the deviations of the four known values from the mean is $-3$.