Explain the concepts of supply, profit, marginal revenue, and shutdown point in the context of a firm's cost curves.

5.2.2. To make a normal profit, the firm should produce where Average Revenue (AR) equals Average Cost (AC). This occurs at point 'b' on the graph, which corresponds to a quantity of 40 units.

5.2.3. Marginal revenue is the additional revenue a firm earns from selling one more unit of a good or service.

5.2.4. The producer would be reluctant to produce 30 units or less because at this quantity (and any quantity below it), the market price (AR=MR=D1) is below the Average Variable Cost (AVC). This means the firm is not even covering its variable costs of production, and it would minimize its losses by shutting down in the short run rather than continuing to produce.