Step-by-step explanation:
Initial fitness is P. Now after the solitary individual being used is social mutant, then the solitary animal drops fitness by B
In such case, the net fitness of Solitary would be ;
P-B
Now the costs (C) for finding a new animal and training it;
P+B-C
Now when the two social types interact, they have a 1/2 chance of being behind the other when a predator attacks
Safest when solitary
P+B/2-B/2-C = P-C
Since P-C would be less than P so the initial condition was better than this one