1)
What is "Ru'ach Elokim"?
1.
Radak citing Targum Yonasan: It is the Ru'ach Ra'ah mentioned above (verse 14)
2)
How did David's music help Sha'ul?
1.
Malbim: (a) It relieved him of his internal distress. (b) [His sadness] was reversed to a trait of Simchah. (c) The Ru'ach Ra'ah departed.