378 miles to 15 gallons of gas

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

Find the roots of the equation below. x^2 - 6 + 9 = 0

Need on this one asap im almost done with this subject