Velma Is in a Train Headed North Past Mort at 30

Multiple Choice

Velma is in a train headed north past Mort at 30 m/s. Velma has a slingshot that can shoot pebbles at 40 m/s. Velma shoots a pebble toward the rear of the train. Velma observes the pebble's velocity to be

A) 70 m/s south.
B) 10 m/s south.
C) 10 m/s north.
D) 40 m/s south.
E) 70 m/s north.