Lure (GTA IV)

Francis is in trouble: although Niko killed Clarence, his organization is still strong. Now, Niko has to kill one of Clarence's drug dealers.

Go to the car on the East River, which has ammo for the sniper rifle. Drive up to the building across from the dealer's apartment and make your way to the roof. Once you get to the vantage point, look into the scope. The dealer is watching TV and can't be seen through the window. You'll see a number on the dealer's phone: 545-555-0122. If you don't take action, eventually Francis will call you with the number. Call it and the dealer will get up to answer the phone. Aim the scope at his head and pull the trigger. After that, get off the roof and back to the street.