A number regarding afternoon meal (3,3,3)

I believe the answer is:

tea for two

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'a number' is the definition.
(I have seen 'Musical number' mean 'tea for two' so perhaps 'number' could also mean 'tea for two')

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for tea for two that I've seen before include "Popular 1925 song (for afternoon drinking companions?)" , "Air" , "Musical number" , "Song from musical No, No, Nanette" .)

I've seen this clue in The Times.

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