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Issue description: Feedback from Matthew White ( mwhitehe@redhat.com  ) 

  In section ch12s11, it does not use the solution given in the class on ch12s05. The question asks "view the recorded events in the previous 30 minutes". This was clearly explained in ch12s05 with the example 'journalctl -since "1 hour" ' . In the solution provided, it used the 'date d "-30 minutes" ' command. Unfortunately, this was not shown anywhere in the class, so many students would not know how to use this rather obscure usage of the 'date' command. Using journalctl with the 'since' and '-before' options was indeed covered in the class, but not the uncommon usage of 'date' shown above, to get their values.  

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