Suppose That the Marginal Benefit of Having a Security Camera

Multiple Choice

Suppose that the marginal benefit of having a security camera in the library is given by MB,at the supermarket is given by MB₁ and at the museum is given by MB₂.All values are per week.
If the weekly marginal cost of security cameras is given by MC,the optimal number of security cameras that should be mounted in the library is ____,the optimal number of security cameras that should be mounted in the supermarket is ____,and the optimal number of security cameras that should be mounted in the museum is ____

A) 30;40;50.
B) 50;50;50.
C) 50;40;30.
D) 40;50;60.