'150 + 50' overwhelms Heather in Administration (8)

I believe the answer is:

clerical

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'150 50 overwhelms heather in administration' is the definition.
I can't tell whether this defines the answer.

'150 50 overwhelms heather' is the wordplay.
'150' becomes 'CL' (Roman numerals).
'50' becomes 'l' (Roman numeral).
'overwhelms' means one lot of letters goes inside another.
'heather' becomes 'erica' (the plant genus Erica includes heather plants).
'cl'+'l'='cll'
'cll' going around 'erica' is 'CLERICAL'.

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(Other definitions for clerical that I've seen before include "White-collar" , "concerned with office" , "Such a life Eliot depicted" , "Relating to the priesthood or office work" , "Relating to the clergy" .)

I've seen this clue in The Independent.

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