Suppose the Dairy Industry Is Made of Up Only by the Three

Suppose the dairy industry is made of up only by the three firms above; Cow Haven, Free Cows, and Happy Cows.
-Refer to the table above. If the cost per unit of advertising is constant at $900, what is the level of advertising per week that maximizes the industry joint profit?

A) 5
B) 4
C) 2
D) 3