Subject: mathqa
Question: if a farmer sells 15 of his chickens , his stock of feed will last for 4 more days than planned , but if he buys 25 more chickens , he will run out of feed 3 days earlier than planned . if no chickens are sold or bought , the farmer will be exactly on schedule . how many chickens does the farmer have ?
Option: 
A: 24
B: 55
C: 49
D: 12
Answer: C