Answer:
the price of a similar substitute or complementary product.
Explanation:
In microeconomics, the cross price elasticity of demand measures how the change in the price of a certain product will affect the quantity demanded for a similar substitute or complementary product whose price doesn't change.
In order to measure the cross price elasticity of demand there must exist a previous relationship between the prices and quantities demanded of the products or services. E.g. a change in the price of movie tickets does not affect the quantity demanded of gasoline, since there is no relationship between them.
You can measure cross price elasticity of substitute products, e.g. coffee and tea, or complementary products, e.g. coffee and sugar. Actually the cross price elasticity is useful for determining how closely related complementary or substitute products are.
the formula for cross price elasticity = % change in quantity demanded of product Y / % change in price of product X.
A negative cross price elasticity means that the products are complementary, while a positive cross price elasticity means that the products are substitutes.