Help me better understand Game Theory

[LockLow34]

This is a theoretical hand:

Assume MP is an unknown player

Hero is UTG with
A[img]/images/graemlins/spade.gif[/img]K[img]/images/graemlins/spade.gif[/img]

Preflop:
UTG calls, MP raises, BB calls, UTG raises, MP calls BB calls

(Pot 4.5 bets)
Flop:
J[img]/images/graemlins/spade.gif[/img] 8[img]/images/graemlins/heart.gif[/img] 4[img]/images/graemlins/spade.gif[/img]

BB checks, UTG bets, MP raises, BB calls, UTG raises, MP raises, BB folds, UTG calls

(Pot 9.5 bets)
Turn:
7[img]/images/graemlins/heart.gif[/img]

UTG checks, MP bets, UTG calls

(Pot 11.5 bets)

question:
With what frequency should one bluff on the river to make calling or folding neutral EV for MP?