You are observing for the growth of mold and anything else that happens to your mixtures. You will have to do the experiment to see exactly what will happen.
The conclusion depends on the results of your experiment. For instance if salt did a better job at preserving the bouillon water mixture than vinegar, your conclusion could be that: "In my experiment I found that one tablespoon of salt is a better preservative than vinegar".
Perhaps you did not leave your mixture long enough, or did not put it in a warm enough spot. The bacteria and mold like warm places to grow. One thing with science experiments, is that they should be repeatable, so try again, see if you get the same results. Eventually the water-bouillon mixtures should get gross.
If you do repeat the experiment, and get the same results, you should try to figure out why nothing happened. Perhaps the bouillon cubes you used have too many preservatives. In this case your conclusion could be that the preservatives used in bouillon cubes has more effect than either vinegar or salt.