Researchers found the demand for milk in Mexico for a particular year can be estimated by the implicit equation ln q = C - 0.678 ln p, where p represents the price of a unit of fluid milk and C represents a constant that can be calculated uniquely for a particular year. Here q represents the annual per capita fluid milk demand.

(a) Use implicit differentiation to calculate and interpret the elasticity of demand. (Recall from the previous section that elasticity of demand is E = -(p/q) · dq/dp.)
(b) Solve the equation for q, then calculate the elasticity of demand.