A square playground has side (a+b) metres. Another square playground has side (a−b) metres, where a>b>0.
a. (i) Find, in simplest polynomial form, the difference between the areas of the two playgrounds.
b. (ii) If a=7 m and b=3 m, calculate the numeric value of the difference in areas.
c. (iii) Explain why your algebraic result in part (i) could also have been obtained without first finding each individual area.