My first instinct was also C but I think you can get B.

You have to develop the equation for the first 40 mile trip with the two different speeds.

Then for the second which will be T = 40/x

Since it is asking for a percentage you can further solve them by expressing in the percent form which should cancel x and then you substitute for y and getet the answer.

I haven't solved it completely yet.

I might be completely wrong but sitting at work and it is past 4pm and I am unable to think straight right now