So what to do?

No Limit Hold'em Cash Game - $0.25/$0.50 Blinds - 6 Players

SB: $49.50
BB: $23.55
UTG: $23.55
MP: $25.45
CO: $50.00
Hero (BTN): $53.70

Reads: We are pretty certain that UTG has a big pair here. BB is unknown.

Preflop: Hero is dealt 6d 7d (6 Players)
UTG raises to $2.00, MP folds, CO calls $2.00, Hero calls $2.00, SB folds, BB calls $1.50

Flop: ($8.25) 6h 5c 4h (4 Players)
BB bets all-in for $21.55, CO folds, UTG calls all-in $21.55, CO folds, Hero...