stakes are 50nl zoom on PS

we are BB w/ :Ad: :Kc:

folded to BTN (villain unknown, full stack) that opens 2.5bb
hero 3bets to 8bb
BTN 4bets to 24bb

hero?

this is a spot where i lose my head... never know the right play and i just decide on the moment.
what would be a good flatting range and a 5bet range?