Item 1.5.3.d.
This doesn't represent a solution. Each star should represent one of the 6 units that add up to 6, and the bars should switch between the different variables. We have one too many bars. An example of a correct diagram would be
\begin{equation*}
*|**||***\text{,}
\end{equation*}
representing that \(x_1 = 1\text{,}\) \(x_2 = 2\text{,}\) \(x_3 = 0\text{,}\) and \(x_4 = 3\text{.}\)