PlO Flop action

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Pot Limit Omaha Ring game
Blinds: $0.50/$1
9 players
Converter

Stack sizes:
UTG: $69.25
UTG+1: $44
MP1: $151.50
MP2: $12.08
MP3: $110
Hero: $177
Button: $19
SB: $68.71
BB: $27.21

Pre-flop: (9 players) Hero is CO with Q[d] 9[s] 8[d] A[s]
2 folds, MP1 calls, 2 folds, Hero calls, Button calls, SB folds, BB checks.

Flop: 7[h] K[s] 5[s] ($4.5, 4 players)
BB checks, MP1 bets $3, Hero calls, Button raises to $16.5, BB folds, MP1 raises to $33, Hero ....., Button calls all-in $1.5.

Assuming MP1 has a set and no intention of folding even if I make my hand on the turn.
I would fold with a blank turn.

EV(call) = (11/42)*(34.5[pot] + 150-34[mp1 stack] ) + (31/42) (-30)
EV(call) = 17,2 %

Chances of hiting on the turn = 26,6 % (Pot equity?)
Chances of Mp1 filling up on the river afert I hit= 25%

Effective Pot equity ? = 20%

Is it correct to use 42 as the number of unknown cards? And how should I
understand the relation between these percentages (Ev and Pot Equity).

* I guess it is correct to call only if I knew MP1 would bet out regardless of whatever hits on the turn.

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[Felonius_Monk]