三十六個人 Thirty Six Men To Lift It
老魔大笑道：「正是，正是。」即點三十六個小妖，入裡面開了庫房門，擡出瓶來。你說那瓶有多大？只得二尺四寸高。怎麼用得三十六個人擡？老魔大笑道：「正是，正是。」即点三十六个小妖，入里面开了库房门，抬出瓶来。你说那瓶有多大？只得二尺四寸高。怎么用得三十六个人抬？
逐句解 Line by line
The old fiend laughed aloud. "Just so, just so."
He has been wrong in every exchange of this scene and remains completely cheerful about it. The book is fond of this kind of demon.
At once he told off thirty-six little fiends to go inside, open the storehouse door, and carry out the bottle.
庫房, a storehouse — the cave has one, with a door that locks, and a treasure kept in it under guard. The domestic detail is doing the same work as the garden did earlier.
How big would you say that bottle was?
The narrator turns and asks the audience directly. This is the storyteller's voice surfacing out of the prose, a leftover from when these chapters were performed aloud, and it is always the signal that a good detail is coming.
Only two chǐ and four cùn tall.
A 尺 chǐ in Ming reckoning is about thirty-two centimetres and a 寸 cùn a tenth of that, so the bottle stands around seventy-seven centimetres — waist high. 只得 keeps 得 at the full dé: merely, no more than.
Then why should it take thirty-six men to lift?
The question the reader was already asking, asked for them. 用得 is the shape where a verb takes 得 and then its object — to require so many — so 得 stays the solid dé, not the light de that hangs a result off a verb.
The bottle is waist-high and needs thirty-six carriers, and the book makes a small performance out of the mismatch before explaining it. That is a genuine storyteller's instinct: put the impossible number in front of the audience, let them object, then answer.
Note also that the answer is coming from the narrator rather than from any character. Nobody in the hall explains the bottle. The reader is being let in on something the demons already know and Wukong does not, which is a rearrangement of who knows what that the chapter has not used until now.