I don't really know what to do here...

PokerStars No-Limit Hold'em, $1.00 BB (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Hero ($125.65)
CO ($161.60)
Button ($94.50)
SB ($36)
BB ($71.20)
UTG ($98.50)

Preflop: Hero is MP with T, Q.
1 fold, Hero raises to $4, CO calls $4, 3 folds.

Flop: ($9.50) 5, 9, A (2 players)
Hero bets $6, CO raises to $18, Hero ???