Inside a train moving east, a child walks 1.5m/s toward the rear (west) measured relative to the train. An observer standing on the ground sees the child moving 0.5m/s east. What is the speed of the train relative to the ground?
a) 1.0m/s west
b) 2.0m/s west
c) 2.0m/s east
d) 1.0m/s east