The given triangle is isosceles, so the two remaining angles in the triangle both have measure xº. The interior angles of any triangle sum to 180º, so that
58º + xº + xº = 180º
58 + 2x = 180
2x = 122
x = 61
Angles y and z are supplementary to angle x, so that
xº + yº = 180º
and
xº + zº = 180º
and consequently, y = z. In particular, we get
y = 180 - 61
y = 119
and so
z = 119
