This is the somewhat final mission in which you're sent out to kill Dutch. You first have to take out some gang members in and around his hideout up in the northern part of tall trees. You'll have the company of an army company, helping you out (a bit). Use cover and shoot the thugs. After you've shot every thug Dutch takes place behind a gattling gun. Shoot the lamp with your sniper rifle and the place he's staying at starts to burn forcing him to move. then follow him up and through a cave, listening to some dialog. At the end there is a cut scene and voila! 90g pops up. easy piece nice and easy.
double spoiler: the story does continue.