In the market for good X there are three buyers, Adam, Bill, and Carolyn. Adam buys 3 units of good X at $4, Bill buys 7 units of good X at $4, and Carolyn buys 8 units of good X at $4. One point on the market demand curve for good X consists of a price of _____________ and a quantity demanded of __________________ units. a. $4; 10 b. $4; 18 c. $4; 15 d. $5; 8 e. none of the above