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Your post requires many explanations from me.
1. The terms "height" and "width" are applied to rectangles mostly.
Nobody uses the terms "height" and "width" for an arbitrary polygon.
2. From this, I conclude (I must conclude) that your polygon is, actually, a rectangle.
If it is so (is it so ??) then why do not use the correct name "rectangle" instead of "polygon" ?
3. Your question is "Find the value of x.", but where is no part of the post explaining what "x" is.
