I can't tell whether the first two parts are right, because you appear to be using information from previous problems, which I have to guess at.
But as I read part (c), not being a veterinarian, it appears that "the desired concentration" is 300 mg/ml, and you are diluting one 3 g vial, not the whole dose. If so, it would seem to be a much simpler problem than you are making it.
But I am not at all sure I am interpreting anything right, without the full context and a knowledge of veterinary procedures.