$\begin{align}  & \overline{x}=\frac{0+x+2+3x+6+4x+8}{4}=4 \\ & \frac{8x+16}{4}=4 \\ & 8x+16=16 \\ & x=0 \\ & \text{The data is }0,2,6,8 \\ & \text{Mean deviation}=\frac{\left| 0-4 \right|+\left| 2-4 \right|+\left| 6-4 \right|+\left| 8-4 \right|}{4} \\ & \text{Mean deviation}=\frac{4+2+2+4}{4}=\frac{12}{4}=3 \\\end{align}$