The mass of 4 children, Shannon, Victoria, Valen and Mark were taken. Only 3 children can be weighed at one time. Shannon, Victoria and Valen weighed a total of 64 kg. Victoria, Valen and Mark weighed a total of 96 kg. Shannon, Valen and Mark weighed a total of 116 kg. Shannon, Victoria, and Mark weighed a total of 144 kg. What is the average mass of the 4 children?
Shannon + Victoria + Valen = 64 --- (1)
Victoria + Valen + Mark = 96 --- (2)
Shannon + Valen + Mark = 116 --- (3)
Shannon + Victoria + Mark = 144 --- (4)

(1) + (2) + (3) + (4)
3(Shannon + Victoria + Valen + Mark) = 64 + 96 + 116 + 144
3(Shannon + Victoria + Valen + Mark) = 420
Shannon + Victoria + Valen + Mark = 420 ÷ 3 = 140

Total mass of the 4 children = 140

Average mass of the 4 children
= 140 ÷ 4
= 35

Answer(s): 35 kg