5. At an Asian mobile service provider, the demand for voice calls had an own-price elasticity of -0.085 and cross-price elasticity with respect to the price of short message service (SMS) of -0.078. The demand for SMS had an own-price elasticity of -0.03 and cross-price elasticity with respect to the price of voice calls of -0.003. (Source: Youngsoo Kim, Rahul Telang, William B. Vogt, and Ramayya Krishnan, "An Empirical Analysis of Mobile Voice Service and SMS: A Structural Model", Management Science, Vol. 56 No. 2, February 2010, 234-252.) (a) For which service was the demand more price inelastic? (b) How would you describe the relation between the demands for voice calls and SMS? Are they (i) complements, or (ii) substitutes? (c) Which is the relatively stronger complement/substitute? (i) SMS for voice calls, or (ii) Voice calls for SMS