Farmer Archie has 4 rabbits. The mass of Rabbit U is the same as the average mass of the 4 rabbits. Rabbit V weighs 8 kg less than the average mass of the 4 rabbits. The mass of Rabbit W is 10 kg more than the average mass of the 4 rabbits. The mass of Rabbit X is 9 kg. Find the total mass of the 4 rabbits.
Let 1 u be the average mass of each rabbit.

Total mass of 4 rabbits
= 4 x 1 u
= 4 u

Mass of Rabbit U = 1 u
Mass of Rabbit V = 1 u - 8
Mass of Rabbit W = 1 u + 10
Mass of Rabbit X = 9 kg

Total mass of the 4 rabbits
= 1 u + (1 u - 8) + (1 u + 10) + 9 
= 3 u - 8 + 10 + 9
= 3 u + 11

4 u = 3 u + 11
4 u - 3 u = 11

1 u = 11

Total mass of the 4 rabbits
= 4 u
= 4 x 11
= 44 kg

Answer(s): 44 kg