Answer
$\bf{H}$
Work Step by Step
Here, $180^{\circ}=\angle z=+123^{\circ}\\ \angle z=57^{\circ}$
The given triangle is an isosceles triangle, so the base angles will be congruent.
Next, we will find the measure of $\angle y$
$\angle y+57^{\circ}+57^{\circ}=180^{\circ}\\\angle y+114=180^{\circ} \\\angle y=66^{\circ}$
Therefore, the correct option is $\bf{H}$.
