"When I was a school teacher I made $17,000 (£11,330) the first year, $18,100 (£12,000) the next year. And on that one commercial I made about $47,000 (£31,330). And this was 20 years ago. One 45 minute session in the studio I made more than in two years of teaching." Teacher-turned-rocker Sheryl Crow is stunned by the royalty payments she received from a jingle she made for MCDonald's in the early 1990s.