Farmer Seth has 4 roosters. The mass of Rooster H is the same as the average mass of the 4 roosters. Rooster J weighs 3 kg less than the average mass of the 4 roosters. The mass of Rooster K is 5 kg more than the average mass of the 4 roosters. The mass of Rooster L is 9 kg. Find the total mass of the 4 roosters.
Let 1 u be the average mass of each rooster.

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

Mass of Rooster H = 1 u
Mass of Rooster J = 1 u - 3
Mass of Rooster K = 1 u + 5
Mass of Rooster L = 9 kg

Total mass of the 4 roosters
= 1 u + (1 u - 3) + (1 u + 5) + 9 
= 3 u - 3 + 5 + 9
= 3 u + 11

4 u = 3 u + 11
4 u - 3 u = 11

1 u = 11

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

Answer(s): 44 kg