How to extract the most here?

Party Poker No-Limit Hold'em, $ BB (9 handed) FTR converter on zerodivide.cx

BB ($97.50)
UTG ($311.22)
UTG+1 ($128.95)
Hero ($106.40)
MP2 ($171.80)
MP3 ($128.10)
CO ($101.50)
Button ($108.80)
SB ($138.80)

Preflop: Hero is MP1 with 6:heart:, 6:spade:. SB posts a blind of $0.50.
UTG calls $1, 1 fold, Hero calls $1, 1 fold, MP3 calls $1, 1 fold, Button calls $1, 1 fold, BB checks.

Flop: ($5.50) 6:club:, 9:diamond:, 8:heart: (5 players)
BB checks, UTG checks, Hero bets $4, MP3 calls $4, Button raises to $16, BB folds, UTG folds, Hero raises to $40, MP3 folds, Button folds.

Final Pot: $65.50

Results in white below:
No showdown. Hero wins $65.50.

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OK, so should I just have called his raise on that board? I was thinking about he was on some kind of two pairs because of his loose style, so I decided to raise and I was sure he would call if he would've been holding two pairs. How should I react on the str8 draws here?