You and CO are both tags.
1. CO raises to 3.5x BB preflop, you call from the BB with
[9d].
2. Flop
[6d][2h], pot 7BB. You check, he bets 6 BB, and you CR to 18 BB. CO calls.
3. Turn
, pot 43BB. You each have 80 BB behind, what's your move here and why?
The better player should win the race. Always.