Exactly what's needed, impartial article on piece of work (4,3,3)
I believe the answer is:
just the job
'exactly what's needed' is the definition.
(just the job means the very thing needed)
'impartial article on piece of work' is the wordplay.
'impartial' becomes 'just' (associated in meaning).
'article' becomes 'the' (the definite article in English).
'on' means one lot of letters go next to another.
'piece of work' becomes 'job' (a job is a task or piece of work).
'just'+'the'+'job'='JUST THE JOB'
(Other definitions for just the job that I've seen before include "Exactly what was required" , "Exact requirement" , "fine!" , "The position is all" , "The very thing" .)