How does Trailhead verify the completion of the Challenge?

Continue to receive the following error message "Could not find a Permission Set named 'Trailhead' that has the 'Two-Factor Authentication for User Interface Logins' permission enabled.".  I have created the following: new developer edition, new user,  and new permission set with required 'Two Factor Authentication for User Interface Logins' ticked.  I then assigned the permission set to the new user, logged out, logged back in as the new user and was successfully able to log in using 2FA.  I am logged in to the same developer edition that I used to create user and set.

There is problem with my  developer org. A code which is just a copy paste of the code provided in trailhead: Quick start Apex: Add a method to the class. (https://developer.salesforce.com/trailhead/project/quickstart-apex/quickstart-apex-2) is not getting saved.

However we tried this code in my friends org, it got saved and she got the points.

I completed the steps as instructed.  The workflow rule and Process Builder work in the app. When I click Verify on Trailhead, I get the following error.  

Step Not yet complete... here's what's wrong: 
The validation rule does not appear to have the correct error formula. Make sure Exhaust Port Inspectors have > 150% utilization' 
Note: you may run into errors if you've skipped previous steps.

Here is my validation rule:   AND ( Name = "Exhaust Port Inspector", Utilization__c < 1.5)

I'm very puzzled that it works in the app, but is returning a verify error 

 

How does Trailhead verify the completion of the Challenge?

I need to remove Email and phone verification code in my account so please give detais in step by step procedure