What is the area of this quadrilateral?

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

Add the two expressions 3.8b - 7 and 2.9b + 9 enter your answer in simplified form

Having a hard time understanding this question (see attachment).