Question 442589
As you know, the area of a parallelogram = {{{b*h}}}. It seems as though we need more information to do this.  Please update your question so that I am able to help you further.
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It seems as though from your description that the base is (2x+6) as well as the height.

Knowing this, {{{(2x+6)*(2x+6) = 4x^2 + 24x + 36 = 108}}}

Then, {{{4x^2+24x -72 = 0}}}. 
*[invoke quadratic "x", 4, 24, -72 ]

Then {{{x =  2.1962}}}

So 2*2.1962 + 6 = 10.393

So the base and height is 10.393 miles.

To check, 10.393 * 10.393 = 108.01 miles.

Close enough. Haha.

Let me know if you figure out if the height or base is something other than (2x+6).