The mass of 4 children, Shiyun, Linda, Glen and Brandon were taken. Only 3 children can be weighed at one time. Shiyun, Linda and Glen weighed a total of 56 kg. Linda, Glen and Brandon weighed a total of 104 kg. Shiyun, Glen and Brandon weighed a total of 119 kg. Shiyun, Linda, and Brandon weighed a total of 93 kg. What is the average mass of the 4 children?
Shiyun + Linda + Glen = 56 --- (1)
Linda + Glen + Brandon = 104 --- (2)
Shiyun + Glen + Brandon = 119 --- (3)
Shiyun + Linda + Brandon = 93 --- (4)

(1) + (2) + (3) + (4)
3(Shiyun + Linda + Glen + Brandon) = 56 + 104 + 119 + 93
3(Shiyun + Linda + Glen + Brandon) = 372
Shiyun + Linda + Glen + Brandon = 372 ÷ 3 = 124

Total mass of the 4 children = 124

Average mass of the 4 children
= 124 ÷ 4
= 31

Answer(s): 31 kg