289 miles on 10 gallons, whats the unit rate

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

Anyone know? will mark brainliest if correct

What’s 8y+48 and factor each expression completely