Answer:
a. market demand and market supply
b. marginal cost.
c.greater than average total cost
fall as new firms enter the market.
Step-by-step explanation:
Equilibrium price is determined where the demand curve intersects the supply curve.
In a competitive market, market price is usually set by the market forces.
A firm maximises profit where marginal cost = marginal revenue.
A firm is making economic profit where price is greater than average total cost. When firms are making economic profit in the short rub , firms enter into the industry in the long run, this drives prices down and wipes out the economic profit. Firms can only enter into industry easily if there are no or low barriers to entry. E.g. in a competitive market.
Therefore, in the long run, industries with low or no barriers to entry or exit of firms make normal profit.
In the short run, a firm should shut down if price is less than average variable cost.
I hope my answer helps you.