Answer:
The income elasticity of demand measures for a given price, the PERCENTAGE CHANGE in quantity demanded divided by the PERCENTAGE CHANGE IN income
If a decrease in the price of one good causes a decrease in demand for another good, the two goods are SUBSTITUTES
Explanation:
In general terms, income elasticity of demand measures the degree of responsiveness of the quantity demanded for a good or service to a change in income.
Substitute goods are goods that have a direct relationship to each other, that is, an increase in price of a particular goods/service would lead to an increase in demand for the other (its substitute)