Area of A: 3x
Area of B: 21
Area of C: x^2
Area of D: 7x
Total area of all four rectangles: x^2 + 10x + 21
I'm not sure what's meant by "sum of the area of the large rectangle", but I believe the point of this exercise is to draw the relationship
[tex](x+3)(x+7)=x^2+3x+7x+21=x^2+10x+21[/tex]
which is entirely a consequence of the distributive property of multiplication.
