Villain hasn't been at the table long so no reads. Not sure about the flop donk, pretty sure I have to call the raise.

Full Tilt Poker
No Limit Holdem Ring game
Blinds: $1/$2
4 players
Converter

Stack sizes:
Hero: $216.40
Button: $202.75
SB: $234.50
BB: $167.40

Pre-flop: (4 players) Hero is UTG with 5 5
Hero calls, Button raises to $9, SB calls, BB folds, Hero calls.

Flop: 6 4 7 ($29, 3 players)
SB checks, Hero bets $16, Button raises to $40, SB folds, Hero ???