How far the eagle flew on the motorway? (7)

I believe the answer is:

mileage

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'how far the' is the definition.
I can't tell whether this defines the answer.

'eagle flew on the motorway?' is the wordplay.
'flew' is an anagram indicator (I've seen 'fly' mean this).
'on' indicates putting letters inside (as in clothing \'on\' a person).
'the motorway?' becomes 'mi' (resembles M1, English motorway**).
'eagle' with letters rearranged gives 'leage'.
'leage' going around 'mi' is 'MILEAGE'.

Can you help me to learn more?

(Other definitions for mileage that I've seen before include "travel allowance" , "Benefit" , "Distance travelled" .)

I've seen this clue in the Evening Standard.

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