Isaac made all these rectangles with 24cm lengths of string. this implies that the perimeter of all these rectangles are equal

The correct question is 
Isaac made all these rectangles with 24cm lengths of string. This implies that the perimeter of all these rectangles are equal. What do we observe about the sum of the length and the width?

Let
x> the length of rectangle
y> the width of rectangle

we know that
[perimeter of rectangle]=2x+2y
24=2x+2y> 12=x+y

the answer is

it is observed that in all the rectangles the sum of its length and its width will be equal to 12

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