First of all, you need to recognize that ∠GHE and ∠AHD are "vertical" angles, so they are equal.
Then, you need to recognize that ∠AHD and ∠AHK are complementary angles.
Then you have
.. ∠AHD +∠AHK = 90
.. ∠GHE +∠AHK = 90
.. (60 -x) +(2x -6) = 90
Now, you have a linear equation in x that is easily solved.
.. x +54 = 90 . . . . . collect terms
.. x = 36 . . . . . . . . . subtract 54 . . . . . . . . . matches selection B*
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* except that the answer is actually 36, not 36°. The variable x is used in an expression to which the units "degrees" are attached. x is a pure number; x° is 36°.