Farmer Howard has 4 rabbits. The mass of Rabbit H is the same as the average mass of the 4 rabbits. Rabbit J weighs 7 kg less than the average mass of the 4 rabbits. The mass of Rabbit K is 8 kg more than the average mass of the 4 rabbits. The mass of Rabbit L is 7 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 - 7
Mass of Rabbit K = 1 u + 8
Mass of Rabbit L = 7 kg

Total mass of the 4 rabbits
= 1 u + (1 u - 7) + (1 u + 8) + 7 
= 3 u - 7 + 8 + 7
= 3 u + 8

4 u = 3 u + 8
4 u - 3 u = 8

1 u = 8

Total mass of the 4 rabbits
= 4 u
= 4 x 8
= 32 kg

Answer(s): 32 kg