Stuck on "Create a Guest Administrator." Any way I try to create the user, I do not see the Salesforce Administrator item in my Profile dropdown of the New User screen, nor do I see the "Salesforce" item in the User License dropdown. I can see Salesforce Administrator under "Profiles."

Appreciate any help, thanks.

I am practicing on trailhead via using my developer org. The chalenging asked me to Create a Guest Administrator and deactivate it. I am currenly the System Administrator of my developer org. We have only one license for System Administrator. How should we solve this issue in order to:
Create a new user using the System Administrator profile and then deactivate that user to preserve the licenses in your org.The new user must use the System Administrator Profile.
The username for the new user must include 'guestadmin' somewhere in it.
The new user must be inactive.
I need some hints or advices. Thanks.