Part (i): You have brought in the point that you can equate the 2 expressions because they are opposite sides of a rectangle and they are therefore the same. You have also explained how you go about balancing the equation. This could be further enhanced if you use terms like "balancing".Part (ii): The unit, "cm^2" should be read as "square centimetre". The substitution is clearly explained (though you could use the term "substitute"). You have also been consistently reminding the viewer you are making reference to information already known. Good.Part (iii): You have also clearly explained how convert from 1 m^2 to 1000 cm^2. Good.