Let the number of chickens be x and that the number of rabbits be y
So, the equation would be
x+y = 72. --Eq.1
4x + 2y = 200 --Eq.2
Eq.1 can also be written as
2x+2y = 144 --Eq.3
Eq.2 - Eq.3
4x -2x+2y -2y = 200-144
2x = 56
x = 28
So, the number of chickens = 28
Number of rabbits = 72-28 = 44