Answer:
The answer is: Ask your supervisor if you can be late for the meeting.
Explanation:
A golden rule in customer service is "treat your customers as you would like to be treated if you were the customer".
So imagine yourself in the customer's position. Would you like your question answered as soon as possible, or would you rather wait around someone else's office wasting your time? It´s not very hard to decide.
Any supervisor will understand if you are going to be late because you are helping a customer.