Answer:
5 to 9 members
Explanation:
Optimal number is simply known to be the best or favorable or required number at a particular point in time.
Normally, every work, especially works that related to sport use to have the required number of people that can work with them at a particular time, most especially when going for a game.
In this case, the expert suggested that, the optimal number of members for a team should be within 5 to 9. And this should include all the needed personnel.