A 15% increase in the price of butter leads to a 10% decrease in the quantity demanded of bread. Calculate the cross-price elasticity of demand and determine the relationship between butter and bread.

• A. 0.67, indicating they are substitutes.
• B. -0.67, indicating they are complements.
• C. -1.5, indicating they are complements.
• D. 1.5, indicating they are substitutes.

Answer: (B)