Who couldn't find the hotel? is the correct answer. It is important to note the rule of use of pronouns as it applies to Who and Whom.
Who functions as a subject while Whom functions as an object. This means that when the verb is being performed, you use Who. If however, the action is received, you use Whom.
See the link below for more about who and whom:
https://brainly.com/question/139669