The hose going to the Power Brake Booster is a Vacuum Hose/Line.
The Hose comming from the Intake Manifold to the front of the Engine and most likely the Inlet/Intake Air Hose/Line for the Vacuum Pump.

The 2 hoses with the; the ones the other Member said have the check valves in them should go to the Vacuum Pump. Click on the picture and enlarge it.

http://www.***************/search/product.aspx?sid=hzo31d5550ncxx553jidel55&makeid=800016@Mercedes&modelid=1193666@300D&year=1976&cid=vacuum@vacuum&gid=5172@Vacuum%20Pump

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84 300D, 82 Volvo 244Gl Diesel