The mass of 4 children, Zoe, Marion, Reggie and Elijah were taken. Only 3 children can be weighed at one time. Zoe, Marion and Reggie weighed a total of 74 kg. Marion, Reggie and Elijah weighed a total of 111 kg. Zoe, Reggie and Elijah weighed a total of 74 kg. Zoe, Marion, and Elijah weighed a total of 77 kg. What is the average mass of the 4 children?
Zoe + Marion + Reggie = 74 --- (1)
Marion + Reggie + Elijah = 111 --- (2)
Zoe + Reggie + Elijah = 74 --- (3)
Zoe + Marion + Elijah = 77 --- (4)

(1) + (2) + (3) + (4)
3(Zoe + Marion + Reggie + Elijah) = 74 + 111 + 74 + 77
3(Zoe + Marion + Reggie + Elijah) = 336
Zoe + Marion + Reggie + Elijah = 336 ÷ 3 = 112

Total mass of the 4 children = 112

Average mass of the 4 children
= 112 ÷ 4
= 28

Answer(s): 28 kg