These are the slides of the second lesson for the course of applied microeconomics. The deal with firms: - Firms' decision problem, profit maximization, revenue, perfectly competitive firm, cost function, supply curve, marginal cost, average cost, profits, long run supply curve, sunk costs, shutdown decision. - Two practical examples: desk manufacturer, effect of 1 dollar tax on the marginal costs, increase in demand, decrease in supply, prices, price, diary milk.