Answer
B
Work Step by Step
If the taxi was directly between John's home and the airport when it started, then it was 5 miles from the airport. (10-5=5). This is the closest the taxi could have been to the airport.
If John's house is between the starting point of the taxi and the airport, then the taxi started 15 miles from the airport. (10+5=15) This is the farthest the taxi could have been from the airport.