Answer:
I think the answer might be B, which could be a trick, because it's asking what the rate is.
If the question was asking for the total amount of gasoline used over the course of 100km, then I think it would be A.
Explanation:
Distance ÷ Rate = Amount
125km ÷ 9.6L/km = 13L/km
100km ÷ 9.6L/km = 10.4L/km