Final answer:
The direct speech 'The master said to his servant, "Open the door"' is converted to indirect speech as 'The master told his servant to open the door.'
Step-by-step explanation:
The sentence "The master said to his servant, 'Open the door'" in indirect speech would be reported as "The master told his servant to open the door." When changing from direct to indirect speech, the request is typically embedded in the reporting verb and given in the form of a command or a request followed by a to-infinitive verb phrase.