The approach is systematic and the description is very clear. You have also reminded the viewer the need to make reference to the conditions given when looking for value for x. You've also described how you have systematically arrived at the pair of factors that result at 20. Good. On the other hand, what happens if the value given is very huge? Then such comparison would not be effective or efficient. Algebra would be a better choice."m^2" should be read as "square metre"The conversion is clearly explained - from single unit conversion followed by working on the area found.