Use the Following to Answer Questions :
Scenario: the Decision

Use the following to answer questions :
Scenario: The Decision to Hire Labour
Assume that both the product market and the labour market are perfectly competitive.The price of this firm's product is $5.The firm's total product with respect to labour is given in the table that follows. $\begin{array}{llcc} \hline \text { Quantity } & \\ \text { of Labour } & \text { Quantity } \\ \text { (workers) } & \text {of Output }\\\hline 0&0\\1 &7\\2 &13\\3&18\\4&21\\\hline\end{array}$

-(Scenario: The Decision to Hire Labour) Use Scenario: The Decision to Hire Labour.The marginal product of the fourth worker is:

A) 7
B) 21
C) 3
D) 15