Farmer Billy has 4 rabbits. The mass of Rabbit H is the same as the average mass of the 4 rabbits. Rabbit J weighs 1 kg less than the average mass of the 4 rabbits. The mass of Rabbit K is 10 kg more than the average mass of the 4 rabbits. The mass of Rabbit L is 8 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 H = 1 u
Mass of Rabbit J = 1 u - 1
Mass of Rabbit K = 1 u + 10
Mass of Rabbit L = 8 kg

Total mass of the 4 rabbits
= 1 u + (1 u - 1) + (1 u + 10) + 8 
= 3 u - 1 + 10 + 8
= 3 u + 17

4 u = 3 u + 17
4 u - 3 u = 17

1 u = 17

Total mass of the 4 rabbits
= 4 u
= 4 x 17
= 68 kg

Answer(s): 68 kg