Opp and I are both playing loose passive, hes not a maniac, hasnt shown any signs of being tricky, and doesnt appear to think past his own cards.I dont recall him raising many hands preflop, maybe*15-20%ish? ..we are both open limping almost all hands to the flop. Hes has only bet-lead out like 2 times outa say roughly 20 hands oop, and I folded both. He has never double or trippled barreled. Also note that he should have no reason to beleive im going to bet this flop, im checking almost all of them because the two times I tried bluffing he called, (sorry i cant remember what he had both those times, the most important information and i forget,sigh). Im really lost what range i should put him on here. As if he has 2 pairs,sets and overpairs, its a auto fold. But why should i rule out str8 & flush draws, and possibly* smaller pairs, in that case ...maybe I should call. Please tell me what you think is best and why you think that.

Seat 1: Hero (2046 in chips)
Seat 2: Opp (954 in chips)
Hero: posts small blind 15
Opp: posts big blind 30
*** HOLE CARDS ***
Dealt to Hero [6d 9c]
Hero: calls 15
Opp: checks
*** FLOP *** [8s 6s 3h]
Opp: checks
Hero: bets 60
Opp: raises 120 to 180
Hero??