In the Market for Good X There Are Three Buyers,Adam,Bill,and

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.A point on the market demand curve consists of the following price-quantity combination:

A) $4, 10
B) $4, 18
C) $4, 15
D) $5, 8
E) none of the above