50nl AJ tough river spot

[ReNoRyan]

He has been pretty loose passive, limps a ton but not very agro.
Poker Stars - No Limit Hold'em Cash Game - $0.25/$0.50 Blinds - 6 Players - (LegoPoker HH Converter)

SB: $40.85
BB: $30.25
UTG: $101.40
<font color="black">Hero (MP): $45.75</font>
CO: $48.60
BTN: $49.45

<font color="black">Preflop:</font> Hero is dealt J[img]/images/graemlins/diamond.gif[/img] A[img]/images/graemlins/heart.gif[/img] (6 Players)
UTG folds, <font color="red">Hero raises to $2.00</font>, 3 folds, BB calls $1.50

<font color="black">Flop:</font> ($4.25) 4[img]/images/graemlins/spade.gif[/img] 2[img]/images/graemlins/club.gif[/img] 7[img]/images/graemlins/spade.gif[/img] (2 Players)
BB checks, <font color="red">Hero bets $3.50</font>, BB calls $3.50

<font color="black">Turn:</font> ($11.25) 3[img]/images/graemlins/diamond.gif[/img] (2 Players)
BB checks, Hero checks

<font color="black">River:</font> ($11.25) A[img]/images/graemlins/club.gif[/img] (2 Players)
<font color="red">BB bets $7.50</font>, Hero ???

Hows my line so far and what do you do on this river, what do you put villian on??