please give through answer with explanation

$.$ Considering the group $\{$n$1,$ n$2,$ n$3,$ n$4,$ n$5,$ n$7\}$ of the social network in Figure $1,$ what is the group centrality $($using degree centrality as measurement$)?$

b$.$ Considering the group $\{$n$1,$ n$4,$ n$5,$ n$6,$ n$7\}$ of the social network in Figure $1,$ what is the group centrality $($using degree centrality as measurement$)?$

c$.$ What does it tell you about the differences between these two groups?