Please help this is urgent!!

Which is an equation for the nth terms of the sequence 12,15,18,21

What is the sum of these mixed numbers 2 1/8 + 4 3/8

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