The manager of the sell-rite drug store accidentally mismarked a shipment of 20 pound bags of charcoal at $5.38 instead of the regular price of $6.18. In a week, a total of 200 bags of charcoal was sold. The store normally sells an average of 160 bags per week. What is the store's arc elasticity of demand for charcoal? Also make an economic interpretation of the elasticity firgure.