In a poultry farm having hens and pigs, Rohan can see 84 heads and 282 legs. How many hens are there?

27

As, the poultry farms have hens and pigs, and, these have 1 head each so the equation formed will be as follows:

H + P = 84 -------1st equation

As, hens have 2 legs and pigs have 4, the equation formed will be as follows:

2H + 4P = 282 --------2nd equation

Solving the 2 equations:

H + P = 84

Multiplying the above equation with 2 

2H + 2P = 168 --------(A)

2H + 4P = 282  --------(B)

Subtracting (A) from (B)

2H + 4P - 2H - 2P = 282 -168

2P = 114

P = 57

H + P = 84 

57 + H = 84

H = 27

Thus, 27 hens were there.