How many crammed into exit? (6)

I believe the answer is:

eleven

I'm a little stuck... Click here to teach me more about this clue!

'how many' is the definition.
'eleven' can be an answer for 'many' (example). I am not certain of the 'how' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for eleven that I've seen before include "Number on a soccer team" , "Number, on a team perhaps" , "Smallest positive three-syllable integer" , "one by one?" , "Prime number" .)

I've seen this clue in The Daily Mail.

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