Answer:
C) any price greater than or equal to $30 and less than or equal to $50
Explanation:
$50 represents the highest amount the student is willing to buy the textbook. She would be willing to buy the textbook at any price equal or below $50.
$30 represents the lowest amount the publisher is willing to sell his textbook. He would accept any price equal or greater than $30.
For an efficient trade to take place, the price of the textbook has to be between $30 And $50.
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