What is the meaning of "vi'Chi"?
Rashi: Shlomo will live.
Radak: The king will give to the Oni from his wealth, and the Oni will live. This is like "v'Chei Achicha Imach" (Vayikra 25:36).
Malbim: The Oni will live, since the king will save him from his oppressor.
Who will give gold to whom?
Rashi: Hashem will give to Shlomo - "Gam Osher Gam Kavod Asher Lo Hayah Chamocha" (Melachim I, 3:13).
Radak, Malbim: The king will give to the Oni.
What is "mi'Zahav Sheva"?
Radak, Malbim: From the gold that they bring to him from Sheva - "Malchei Sheva u'Sva Eshkar Yakrivu" (verse 10). Malbim - because his wealth is in the merit of his Tzedakah, he will increase to give from it to the Oni.
Who will pray for whom?
Rashi: This is Hashem's Brachah to him; it is called Tefilah.
Radak, Malbim: The Oni will always pray for the king.
Will he bless him the entire day?
Radak: He will do so all days.
Why is there a Nun in "Yevarachenhu"?
Radak: This is extra, like we find elsewhere, e.g. Yidrechenhu 1 .
I did not find this word anywhere. Perhaps the text should say "Ya'avrenhu" (Yirmeyah 5:22). There, Radak said that the Nun is extra, like here. (PF)
