Answer: B) Its total cost is less than $4000
Step-by-step explanation:
If a competitive firm is selling 500 units of its product at a price of $8 per unit, its total sales of 500units will be $8 × 500 which is $4,000. Since the firm earns a positive profit, this means that its total cost is less than $4000
Since a positive profit was made, it means the total sales(selling price) is definitely greater than cost price. If the cost price is greater than selling price, it means a loss was generated (negative profit) which is not the case here.