First, we notice that the set of data given is already ordered from lowest (5) to highest (18). Then, the median is
[tex]\frac{11+12}{2}=11.5[/tex]
Now, we compute the first and third quartiles:
[tex]\begin{gathered} Q_1=8 \\ Q_3=15 \end{gathered}[/tex]
Finally, the box and whiskers plot is as follows:
