Chidester company concludes the demand function for its product is
Q= 500 - 3P + 2Pr + 0.1 I
where Q is the quantity demanded of its product, P is the price of its product, Pr is the price of its rival product, and I is per capita disposable income. At present, P=$10, Pr=$20, and I=$6000
what is the price elasticity of demand for the firms product?