Figure 9-23
The following diagram shows the domestic demand and domestic supply for a market. Assume that the world price in this market is $120 per unit.
-Refer to Figure 9-23. Producer surplus with free trade is

Question

Figure 9-23
The following diagram shows the domestic demand and domestic supply for a market. Assume that the world price in this market is $120 per unit. 
-Refer to Figure 9-23. Producer surplus with free trade is

Quizplus · Accepted Answer

However, since you've provided an answer "c. $630" as the producer surplus with free trade, I can explain how you would generally arrive at such a conclusion with the appropriate diagram:
Producer surplus is the area above the supply curve and below the market price level, up to the quantity produced. With free trade, the market price is given as the world price, which is $120 in your scenario. To find the producer surplus, you would:
1. Identify the supply curve on the graph.
2. Look for the quantity supplied by domestic producers at the world price of $120.
3. Calculate the area of the triangle or trapezoid (depending on the shape of the supply curve) that is formed by the supply curve, the price line at $120, and the vertical line at the quantity supplied.
The area is typically calculated using the formula for the area of a triangle (1/2 * base * height) or a trapezoid, depending on the shape. The base would be the quantity supplied, and the height would be the difference between the market price ($120) and the lowest point on the supply curve above which production occurs.
Since you've indicated that the correct answer is $630, this would be the area calculated based on the specific supply and demand curves in Figure 9-23. To provide a full answer, one would need to see the actual graph and perform the calculations based on the curves presented.

Figure 9-23 The Following Diagram Shows the Domestic Demand and Domestic Supply