I think this star is the easiest of the whole game.  When you first start the level, you will see two pink bob-ombs.  Talk to one of them to open the cannons.  Run straight along the path, and jump over the fence after the bridge.  There is a large, squareish shaped rock.  Climb to the top of this and jump in the cannon.  Find, in your sights, the island in the sky.  Aim the cannon towards this, then pull down on the joystick to make the cannon face the sky as high as it will go.  Shoot out, and you should fall straight onto the island.  Hit the yellow block and collect the next star.

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