Please consider the effect of the price change (i.e., the sum of the income effect and the substitution effect.) On one good, we cannot answer how the price change would change the quantity demanded of the good. On another good, we can answer how the price change would change the quantity demanded of the good. Answer on which good we cannot answer and how the another good would change: Increase or Decrease.

The good we cannot answer:

How the another good would change: