how does rahim get amir to help sorab, what's amirs response and would amir have helped sorab if rahim didn't tell him to.

When Amir protested and suggested Rahim Khan hire someone to find Sohrab, Rahim Khan was insulted. He told Amir, "I think we both know why it has to be you, don't we?" Then he asked Amir if he had become what Baba feared so many years before, a person who "can't stand up to anything." He said it was his dying wish for Amir personally to bring Sohrab to Peshawar. When Amir continued to refuse, Rahim Khan revealed a monumental secret. Amir and Hassan were half-brothers. Ali was infertile, as evidenced by the fact that his first wife bore him no children, but bore her second husband three daughters. It was Baba who had gotten Sanaubar pregnant, making Hassan his son. Rahim Khan explained that no one but himself, Baba, Ali, and Sanaubar had known about the matter in order to preserve their honor. Hassan never found out. Amir was furious at all of them for keeping the secret. He screamed at Rahim Khan and left the apartment. Later, after a lot of thought, he returned to Rahim Khan's apartment to find him praying and told him he would bring Sohrab to Peshawar. I'm not sure what he would have done had he not been told.