WAEC Economics 2001 Question 14

Use the table below to answer questions 12, 13 and 14.
Units of Variable factor | Total Product
1 | 25
2 | 31
3 | 40
4 | 48
5 | 55
The average product of the variable factor when four units are employed is

1. A.6
2. B.8
3. C.12
4. D.48