Farmer Gabriel has 4 puppies. The mass of Puppy L is the same as the average mass of the 4 puppies. Puppy M weighs 4 kg less than the average mass of the 4 puppies. The mass of Puppy N is 6 kg more than the average mass of the 4 puppies. The mass of Puppy P is 9 kg. Find the total mass of the 4 puppies.
Let 1 u be the average mass of each puppy.

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

Mass of Puppy L = 1 u
Mass of Puppy M = 1 u - 4
Mass of Puppy N = 1 u + 6
Mass of Puppy P = 9 kg

Total mass of the 4 puppies
= 1 u + (1 u - 4) + (1 u + 6) + 9 
= 3 u - 4 + 6 + 9
= 3 u + 11

4 u = 3 u + 11
4 u - 3 u = 11

1 u = 11

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

Answer(s): 44 kg