please answer correct for thumbs up

D(p)=p22p+500 is a demand function for a commodity that is sold at p dollars apiece. (a) Compute the elasticity of demand when the price is $15 per unit. (Round your final answer to the nearest hundredth of a percent if necessary.) (b) Interpret your answer in part (a) in terms of percentages. (Do NOT mention anything about it being elastic/inelastic/unit elasticity - this is not what I'm looking for here. Just explain what this number in part (a) means, in terms of percentages.)