Answer:
Equilibrium quantity of X increases and that of z decreases.
Explanation:
If two goods are substitutes then 1 can be used in the place of the other. As supply of Z falls, we would have market demand to be greater than supply. This brings about a price rise. The price rise will make consumers of Z to want it less and opt for a cheaper good X. Increase in the demand for X causes its supply to rise in the market.
So we would have increase in equilibrium quantity of X and that of Z would fall.