JAMB Economics 2009 Question 17

Use the table below to answer questions 17 and 18.
Unit of capital | Total output (kg)
1 | 16
2 | 64
3 | 126
4 | 212
5 | 425
6 | 684
The marginal product of the 5th unit of capital is

1. A.42
2. B.85
3. C.114
4. D.213