What is the greatest common factor of the terms in the expression 21x-18x+28xy

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, gef and hef are congruent. what is the value of x

Meee i honestly dont know what this question talking about