SOMEONE PLEASE EXPLAIN!!

Four members of a marching band are arranged to form the vertices of a parallelogram. The coordinates of three of the band members are A(−3, 1), B(1, 3), and C(2, −1).

Part 1: Given this information, find all possible coordinates for the fourth band member.

Part 2: How do you know that you have found all possible coordinates? Justify your answer using words, mathematics, and/or patterns as needed.