Worldwide annual sales of smartphones over a five year period were projected to be approximately 9 = -10p + 4,380 million phones at a selling price of Sp per phone. (a) Obtain a formula for the price elasticity of demand E. 10p 4380 - 10p (b) In one year the actual selling price was $291 per phone. What was the corresponding price elasticity of demand? (Round your answer to two decimal places.) E = 1.98 Interpret your answer. (Round your answer to two decimal places.) The demand was going down by about X % per 1% increase in price at that price level. (c) Use your formula for E to determine the selling price that would have resulted in the largest annual revenue. $ what, to the nearest $10 million, would have been the resulting annual revenue? $ million