Figure to get hack's sound support, first to last (8)
I believe the answer is:
eighteen
'first to last' is the definition.
I can't tell whether this definition defines the answer.
'figure to get hack's sound support' is the wordplay.
'figure' becomes 'eight' (eight is a number).
'to get hack's sound' becomes 'een' (I can't justify this - if you can you should give a lot more credence to this answer).
'support' is a charade indicator (letters next to each other) (in a down clue, some letters hold others up).
'eight'+'een'='EIGHTEEN'
Can you help me to learn more?
(Other definitions for eighteen that I've seen before include "Age when one may legally buy alcohol in the UK" , "when boy becomes man?" , "majority number" , "Golf-holes in a round" , "Nine times two" .)