Answer
Option: a. the change in total product divided by the change in the quantity of labor.
Work Step by Step
Marginal Product is given as follows:
$Marginal Product$ = $\frac{Change \ in\ total\ product}{Change\ in\ labor\ input}$
Definition of Marginal Product:
The amount of extra output that a producer gets after adding an additional unit of input is called Marginal Product.
Example:
Suppose, 2 people at a bakery can make 6 cakes in an hour. When an additional cook is hired, the number of cakes cooked in an hour rises to 9. In this case, we increased the input, i.e. labor by one unit (from 2 to 3). Thus, the output (number of cakes baked) increases by $9-6\ = \ 3$. Hence, 3 was the marginal product in this case.
