Final answer:
In market equilibrium, the producer surplus is represented by the area of a triangle, which is calculated as one-half of the base times the height of that triangle on a supply and demand graph.
Step-by-step explanation:
If the market is in equilibrium, the producer surplus equals the area of the triangle formed by the equilibrium price on the y-axis, the actual price received by producers on the supply curve, and the quantity sold on the x-axis. This is typically conceptualized as one-half of the base times the height of that triangle, where the base is the quantity of goods sold, and the height is the difference between the equilibrium price and the lowest price at which producers would still be willing to sell (also interpreted as the cost of production for the marginal producer).
Therefore, the correct answer is: a) One-half base times height. This calculation will give us the area of the triangle representing the producer surplus in a supply and demand graph.