The price elasticity of demand for senior citizens purchasing coffee from McDonald's is −5, while non-senior citizens have a price elasticity of demand equal to −1.25. If it costs McDonald's $0.02 to produce a coffee, the optimal price for a cup of coffee for senior citizens and the resultant marginal cost under third-degree price discrimination are, respectively:
a) $0.016 and $0.20.
b) $0.02 and $0.80.
c) $0.025 and $0.02.
d) $0.10 and $0.02.