First, find the supplementary angle of angle A. Together, they should add up to 180°, which is a straight line.
123°+y°=180°
y°= 180°-123°
y°=57°
The interior angles of a triangle add up to 180°.
58°+57°+x°=180°
115°+x°=180°
x°=65°
The measure of angle x is 65°.