Let the width be x cm.
Then length=3x-4 cm.
Its perimeter is 64 cm.
We know that perimeter of a rectangle= 2(length+width)
So,
2(3x-4+x)=64
6x-8+2x=64
6x+2x=64+8
8x=72
x=9
Therefore,
length=(3×9-4)cm=(27-4)cm=23 cm.
Width=9 cm.
<u>The commutative property is when you can change the order and it will be the same answer.</u>
<u>6 + 8 + 7 = 7 + 8 + 6</u> would be your answer.
I would rather use a ruler but it depends on what you are doing.