Answer:
Normative Social Influence.
Step-by-step explanation:
Normative Social Influence can be defined as social influence that leads a person to conform to the patterns of the group in which they belong. In this concept, a person behaves in a certain manner that attests to the behavior to the group in which they belong with an urge to be accepted by them. A person would conform to their patterns so that he/she may not be ridiculed or made fun of, or declined from the group.
In the given case, Gareth, who was not sure if he liked the concert or not, at last, confirmed to his group of friends who liked the concert. He convinced himself of it so that he may not be made fun of or ridiculed by his friends for not liking the concert.
Thus the correct answer is normative social influence.