1)
Who are "Malchei Arav"?
1.
Rashi: They are [kings of] Araviya. Radak - they dwell in tents, like it says "Lo Yahel Sham Aravi" (Yeshayah 13:20).
2)
Who are "Malchei ha'Erav"?
1.
Rashi: They are [kings of] Sumchavasa 1 of Araviya.
3)
Verse 20 already mentioned "Kol ha'Erev." Why was this repeated?
1.
Radak: Here it explains that they dwell in the Midbar.
