In a tug-of-war game on one campus, 15 students pull on a rope at both ends in an effort to displace the central knot to one side or the other. Two students pull with force 51 N each to the right, four students pull with force 135 N each to the left, five students pull with force 136 N each to the left, three students pull with force 114 N each to the right, and one student pulls with force 188 N to the left. Assuming the positive direction to the right, how big is the net pull on the knot