The correct option is D 10
Total food for 400 person for 31 days = 400×31=12400
Food consume in 28 days = 28×400=11200
Remaining food = 12400−11200=1200
280 person leave the place
so remaining person = 400 - 280 = 120
Hence the no of days will the remaining food last for the remaining person
= 1200120=10days