HELP ME WITH THIS PLEASEEE

Monica build a remote control toy airplane for science project to test the plane she launched it from the top of a building the plane travel a horizontal distance of 50 feet before landing on the ground a quadratic function which models the height of the plane in feet relative to the ground at a horizontal distance of x feet from the building is shown

In the diagram of circle o, what is the measure of zabc?

1.based of the diagrams what is the the value of x? 2.how would you verify your answer for x