Explanation:
I am not sure what you mean by A, B, and C.
the picture does not name the corners or vertices.
but is seemingly asks for the angle x.
remember, the sum of all angles in any triangle is always 180°.
and the sum of all angles around one point on one side of a line is also 180° (as the line cuts a virtual circle in half with its center being the point around which the angles rotate).
when we know all angles except for one, we call the missing angle a supplementary angle (fills up to 180°).
if the angle fills up to 90°, we call that a complementary angle.
so, now look at the triangle. we know 2 angles : the right angle (90°) and the 38° angle.
so, the third angle down left must be
180 - 90 - 38 = 52°
and x is the supplementary angle to 52° :
x = 180 - 52 = 128°