$3.$ Based on the following graph $($which summarizes the demand, marginal revenue, and relevant costs for your product$),$ determine your firm's optimal price, output, and the resulting profits for each of the following scenarios:

a$)$ If you charge the same unit price to all consumers. $(12\mathrm{.}5$ pts$)$

b$)$ If you engage in block pricing. $(12\mathrm{.}5$ pts$)$