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If $ \overline { CB } $ is a diameter in circle $D$, and $ \triangle ABC $ is inscribed in circle $D$ in the figure above, then what is the value of $ x $? (No Calculator)

$ { 17.5 }^{ \circ } $

$ { 20 }^{ \circ } $

$ { 35 }^{ \circ } $

$ { 40 }^{ \circ } $