Rashi Studies (Advanced)

When Rivkah was having difficulty with her pregnancy, why did she go to Sheim and not to her husband Yitzchak or her father-in-law Avraham?

Rashi explains that Eisav would deceive his father into thinking he was righteous by asking him how to separate ma'aser from salt and straw. But it seems obvious; one separates ma'aser from anything by separating off one tenth of it. What was Eisav really asking?

Yitzchak found a hundredfold increase in his crops and became wealthy. But an increase compared to what? At what point in the growing process did the crops increase so dramatically?

Rashi offers three explanations for why "the vision of [Yitzchak's] eyes had dimmed." But the verse before has just stated, "Yitzchak had grown old." Isn't that a good enough reason? And why does Rashi need to bring three different explanations?