In some instances, a case must automatically escalate. Create a workflow rule that will set the escalated flag and send a task to the case owner if a case is not closed and its priority is set to High.

NOTE: Since Workflow rules only fire on record save, normally you would implement this with a time-triggered workflow action.

The workflow rule must be called 'Case Escalate on High Priority'.
The workflow rule must be tied to Case and fire when it is not closed and the Priority is updated to 'High'.
The workflow rule must evaluate on create and when is doesn't meet the criteria but is edited to meet the criteria.
The rule should fire a Field Update action called 'Set Case to Escalated'.
The Field Update action must set the 'Escalated' checkbox field to true.
The rule should fire an Assign Task action with a subject of 'Follow Up on Escalated Case'.
The Assign Task action must assign a task to the owner of the Case.
The Task should have a due date of 'Rule Trigger Date', status 'Not Started' and Priority 'Normal'.

I am having trouble Creating a workflow rule field for this challenge. Can someone please let me know what FIELD, OPERATOR AND VALUE I am suppose to create for this workflow to work 

Hi all, 
I'm a newby in Salesforce so I decided to start learning with the Trailhead. 
I have completed all the challanghes related to the "Getting Started with the Force.com Platform". 
This morning I started with the part 2: "Intro to Visual App Development". 

The fist challenge for Workflow Atuomation is about "Automated Process with Workflow". 
I did the challenge but I receive a failure even if It should seems to run correctly in my Develper Edition Platform. 
Tha error massage received by the check challange button is "Challenge not yet complete... here's what's wrong: Case escalation failed to assign a task to the owner."

I say that all seems to work fine because I edited e case, set up the Priority to High and: 
1) The Escaleted flag was set automatically to true as per the rule action defined
2) I receive a notification about escalation on that case (because I'm the owner of the case as per the task definition field)
3) An activity under the case was automatically created and assigne to me. 

As anyone tha same problem?
Any help would be much appreciated. 
Thank's in advance,
Alvaro.