Which function is the inverse of f(x)=9x-3

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

This question awards 100 ! i really don’t want to fail i will also mark you !

Find the area of the triangle shown 3 by 6