Without seeing the first two parts (a) and (b) of the question, I'm guessing the question concerns titration.
In planning titration, the pH indicator should be chosen so that the colour transition occurs near the equivalence point for the neutralisation reaction. Methyl orange transition occurs between 3.1 to 4.4, and phenolphthalein transition occurs between 8.3 to 10.0 so clearly they will give different values for the titre and different calculated concentrations for the HCl soln. Now, whether the titre will be too low or too high depends on the direction you are coming from. We need the rest of the data from the question, so I leave it to you to work that out.