Which quantity is proportional to 8⁄12

What is the measure of angle z in this figure? enter your answer in the box. z = ° two intersection lines. all four angles formed by the intersecting lines are labeled. clockwise, the angles are labeled 43 degrees, x degrees, y degrees, and z degrees.

Me. i can't figure out this question. give an explanation too. .

Use circumcenter theorem to solve for the given values