9,000!
The farmer has eight cows, since all but that many died.
If a farmer starts with 13 cows and all but 9 die, he would have 9 cows left. The phrase "all but 9" means everything except 9. So, if all the cows except 9 die, those 9 remaining cows are what the farmer has left.
Over 9000!
About half as many cows died as pigs.
Richard Farmer died in 1797.
Jack Farmer died in 1970.
Emily Farmer died in 1905.
Addison Farmer died in 1963.
Over 9000.
The former farmer died.
if you have 4 cows and they die, you now have 0 cows. you don't have negative 4 cows. the answer is 0.
OVER 9000