In a perfectly competitive market, how does a firm decide on the quantity of output to produce in the short run, and how might this decision change in the long run?

In a perfectly competitive market, a firm decides how much to produce by looking at its costs and the price it can get for its product. The firm aims to produce the quantity where its marginal cost, which is the cost of making one more unit, equals the market price. For example, if the price of a product is $10 and the cost to produce one more unit is also $10, the firm will produce that unit because it maximizes profit. In the long run, if firms in the market are making profits, new firms will enter, increasing supply and potentially lowering the price. This might lead the original firms to adjust their output to find a new balance between costs and the market price.