A long passenger train moves at an unknown speed along straight tracks. A passenger on the train measures Car X, traveling on a nearby road, to move 15 m/s east relative to the train. The same passenger measures Car Y on the road to move 25 m/s west relative to the train. A roadside traffic camera fixed to Earth records Car X at 5 m/s east and Car Y at 35 m/s west, both relative to the ground. What is the train’s velocity relative to the ground?
a) 20m/s west
b) 10m/s east
c) 10m/s west
d) 20m/s east