Answer:
C. 40°
Explanation:
From the diagram, in triangle XYZ, XY=XZ=6 units. This means triangle XYZ is isosceles triangle with base YZ.
In isoscels triangle angles adjacent to the base are congruent, so
∠ZYX=∠YZX=70°
The sum of all interior angles in triangle is always 180°, so
∠ZYX+∠YZX+∠ZXY=180°
∠ZXY=180°-70°-70°
∠ZXY=40°
∠ZXY is ∠X, so ∠X=40°