Selection D is appropriate.
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I would write it differently.
.. 180 -x = "supplement of an angle"
.. 2x +20 = "20 more than twice the measure"
These are said to be equal, so I would write it as
.. 180 -x = 2x +20
Of course, adding x to both sides of this equation makes it
.. (2x +20) +x = 180 . . . . . . matches selection D