Hi, working on finishing song 3 for my CD. Had my neighbor play keys to fill in some holes and do a piano solo. My question: What % of songwriting credit does this account for. I've written the lyrics, music, bass, guitars, drums and was basically done but thought that some keys would be good and he's a great player and I want to be fair. Another question..say for example, the song in questions was a hit, would his credit be a percentage of songwriting (10-20?) or a flat fee as a session player. Please forgive my ignorance. Thanks. M.