Part (i): You have clearly explained how you arrived at the equation (and also the rationale behind it). The attempt to explain the solving of equation by balancing during the manipulation is clear.Part (ii):"cm^2" to be read as "square centimetre"The substitution is clearly explained. You could use terms like "substitute" in the explanation. Well, what's the unit of your answer? You've left that out.Part (iii): The conversion is clearly explained. Good. Again, what's the unit of this answer?