The Stop decay company sells an electric toothbrush for $25. Its sales have averaged 8,000 units per month over the past year. Recently, its closest competitor, Decay fighter, reduced the price of its electric toothbrush from $35 to $30. As a result, stop decay's sales declined by 1,500 units per month.
What is the arc cross elasticity of demand between Stop decay's toothbrush and Decay fighter's toothbrush? What does this indicate about the relationship between the two products?