The area is the product of the length and width, so to find the width, you divide the area by the length. This can be done using <em>polynomial long division</em> (shown in the first attachment) or <em>synthetic division</em> (shown in the second attachment).
The width is: 2c² +3c +6 +18/(c -2).
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Only the last step and the final result are shown for synthetic division. The previous steps are calculated exactly the same way. The number on the left is the root of the binomial you're dividing by (2, in this case).