The correct answer is: Only assumption I is implicit.
The statement is an advertisement for X Airways, which is trying to persuade people to fly with them. The statement says that X Airways’ fares are less than train fares. This suggests that people might prefer to travel by air if the fares are reasonable. However, the statement does not say anything about whether people prefer to travel by air in general, or whether they prefer X Airways to other airlines. Therefore, assumption II is not implicit.
Assumption I is implicit because the statement is trying to persuade people to fly with X Airways by saying that their fares are less than train fares. This suggests that people might prefer to travel by air if the fares are reasonable.