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Your play here? What kind of bet do you make and what do you do if you get reraised?

Party Poker No-Limit Hold'em Tourney, Big Blind is t400 (2 handed) converter

Hero (t2315)
Button (t5685)

Preflop: Hero is BB with 5[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/club.gif[/img].
Button calls t200, Hero checks.

Flop: (t800) J[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero ?