JAMB Economics 1987 Question 22

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
What is market demand for the commodity when price is ₦5?

1. A.65 units
2. B.40 units
3. C.30 units
4. D.20 units