The correct option will be : B) 6 cm.
<u><em>Explanation</em></u>
Suppose, the width of the rectangle is
cm.
As, the length is 6 cm longer than the width, so the length will be: 
<u>Formula for the Area of rectangle</u> is:
Given that, the area of a rectangle is 72 cm²
So....

Using zero-product property, we will get...
<em>(Negative value is ignored as width can't be negative)</em>
and

So, the width of the rectangle is 6 cm.