Answer thought to be happily occupied (6)
I believe the answer is:
amused
'be happily occupied' is the definition.
(to amuse someone is to occupy or entertain them)
'answer thought' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'thought' becomes 'mused' (musing is a kind of thinking).
'a'+'mused'='AMUSED'
'to' is the link.
(Other definitions for amused that I've seen before include "Beguiled" , "Medusa (anag)" , "Kept someone entertained" , "was entertaining" , "Victoria reputedly wasn't" .)