how does cross-price elasticity of demand change in substitute goods? I mean, how to tell if it is increase/decrease?

"the change in quantity with respect to a change in price for a supply curve is not equal to the change in quantity with respect to a change in price for a demand curve" how to interpret this statement？

I still can't understand this problem... Can you explain it again?

Is it right that no matter incidence of tax or incidence of subsidy, the incidence falls on customers are the same?