There are 67 ducks and pigs.
∴(x+9)+x=67
2x=67-9
The solution is x=29 (only)
∴ Number of chickens =4*29= 1 16 (only)
Number of pigs =29+9=38 (only)
A chicken has two feet, a duck has two feet and a pig has four feet.
∴ (116 * 2)+(29 * 2)+(38 * 4) = 442 (only)
This farm is 442 feet.