The Potomac Range Corporation manufactures a line of microwave ovens costing $500 each. Its sales have averaged about 6,000 units per month during the past year. In August, Potomac's closest competitor, Spring City Stove Works, cut its price for a closely competitive model from $600 to $450. Potomac noticed that its sale volume declined to 4,500 units per month after Spring City announced its price cut. a. What is the are cross elasticity of demand between Potomac's oven and the competitive Spring City model? b. If Potomac knows that the arc price elasticity of demand for its ovens is - 3.0, what price would Potomac have to charge to sell the same number of units it did before the Spring City price cut?