A Methuen teen was killed Saturday night and her passenger seriously injured when the 2004 Lincoln LS state police said Alexis Spartz was driving northbound on Interstate 495 in Haverhill rolled over and crashed.Police said an off-duty Methuen firefighter, two off-duty troopers and Haverhill firefighters pitched in to free Spartz, 18, and her 19-year-old passenger from the mangled wreck and render first aid.The crash occurred about 6 p.m.