Instructions
Go to the roof of the building where you rescued the hostage. Get out the rocket launcher you picked up on the first floor and look for green dots on your map. These dots are tanks.
Shoot three rockets at one of the tanks. This will destroy it. However, you'll have to go back inside for another launcher with three more rockets. Return to the roof and destroy the second tanks. Remember, it takes all three rockets.
Proceed southeast from the building toward your new objective. When you hit a waterfall, you'll go into the "Crossings" chapter.