Answer:
b. It conveys the mayor's displeasure with the dentist's performance.
Step-by-step explanation:
This is a clearer excerpt from the passage;
"Send the bill," he said.
"To you or to the town?"
The Mayor didn't look at him. He closed the door and said through the screen:
"It's the same thing."
Thus, we could infer from the mayor's action of not looking at him and closing the door mentioned in the passage above as a sign of his displeasure with the dentist's performance.