JAMB Economics 1987 Question 21

Use the following information to answer this question. X, Y and Z are the only three consumers of a commodity. Their respective demand schedules for the commodity are as given below:
X: Price (₦) | Quantity (Units)
0 | 20
2 | 15
5 | 10
10 | 0
Y: Price (₦) | Quantity (Units)
0 | 15
2 | 10
5 | 5
10 | 2
Z: Price (₦) | Quantity (Units)
0 | 40
2 | 30
5 | 15
10 | 5
The market demand curve for the commodity cuts the quantity axis when quantity is

1. A.75 units
2. B.35 units
3. C.7 units
4. D.not determinable from the schedules except when graphed.