Farmer Zeph has 4 puppies. The mass of Puppy S is the same as the average mass of the 4 puppies. Puppy T weighs 7 kg less than the average mass of the 4 puppies. The mass of Puppy U is 10 kg more than the average mass of the 4 puppies. The mass of Puppy V is 12 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 S = 1 u
Mass of Puppy T = 1 u - 7
Mass of Puppy U = 1 u + 10
Mass of Puppy V = 12 kg

Total mass of the 4 puppies
= 1 u + (1 u - 7) + (1 u + 10) + 12 
= 3 u - 7 + 10 + 12
= 3 u + 15

4 u = 3 u + 15
4 u - 3 u = 15

1 u = 15

Total mass of the 4 puppies
= 4 u
= 4 x 15
= 60 kg

Answer(s): 60 kg