Subject verb agreement
Ex1: the child,together with his grandmother and his parents, is going to beach.
Subject- child
Verb - going
Agreement- is (not are)
Sandwich- together with his grandmother and his parents( not to be considered)

Ex2: Frank, accompained by his students, was(were) at the studio.
Noun- singular- frank
So verb- was at the studio- singular

Ex3: His mastery of several sports and social graces makes( make) him a sought- after prom date.
His mastery- singular subject
So makes- singular verb