Each emu has 1 + 2 = 3 heads and legs. Then the flock has 60 / 3 = 20 animals.
This justifies what answer for what question? Q & A: 
Farmer Brown raises emus, large birds. His flock has a total of 60 heads and legs. How many emus are in his flock?
20
Each emu has 1 + 2 = 3 heads and legs. Then the flock has 60 / 3 = 20 animals.
This justifies what answer for what question? Q & A: 
user
Farmer Brown raises emus, large birds. His flock has a total of 60 heads and legs. How many emus are in his flock?
20
assistant
Each emu has 1 + 2 = 3 heads and legs. Then the flock has 60 / 3 = 20 animals.
This justifies what answer for what question? Q & A: 
Farmer Brown raises emus, large birds. His flock has a total of 60 heads and legs. How many emus are in his flock?
20