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 

The challenge as follows:

For purposes of local regulation new customers must be approved by the legal team.

When an Account has the value of 'Prospect' in the Type field, a user will click the 'Submit for Approval' button to launch an approval process. The process will only happen if Type is 'Prospect' and there are more than 500 employees. Upon entry of the process, Type will become 'Pending' and be locked. If approved, Type will be set to 'Customer' and be unlocked. If not approved, Type will be set back to 'Prospect' and will be unlocked.

The Account object's Type field must have the following picklist values: Prospect, Customer, Pending. Before creating the approval process, verify the values in your Account object setup
The approval process name must be 'Approve New Account'.
When user click 'Submit for Approval', the approval must be processed if the Type field is set to 'Prospect' and the value of Employees is greater than 500.
Upon entering the approval process, set the Type field to 'Pending' and lock the record.
Normally the approver would be someone else. In this instance, assign yourself to be the approver.
If approved, set the Type field to 'Customer' and unlock the record.
If not approved, set the Type field back to 'Prospect', and unlock the record.

I am getting error message: Challenge not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Process failed. First exception on row 0; first error: REQUIRED_FIELD_MISSING, missing required field: [nextApproverIds]: [nextApproverIds]

This are the steps I did:

Created approval process called Approve New Account
Criteria Account Type field equals Prospect and Account Employees field greater than 500
Final Approval Actions - Update Type field to Customer
Final Rejection Actions - Update Type field to Prospect

What am I missing that I received the error message?  Please help.

Thanks.