Service area set back a long way away (4)
I believe the answer is:
afar
'a long way away' is the definition.
(I've seen this before)
'service area set back' is the wordplay.
'service' becomes 'raf'.
'area' becomes 'a' (maths abbreviation).
'set back' says the letters should be written backwards.
'raf'+'a'='rafa'
'rafa' written backwards gives 'AFAR'.
(Other definitions for afar that I've seen before include "from baseline to baseline?" , "At a distance (poetic)" , "long way back" , "Many a mile" , "Unusually distant" .)