Final answer:
The net force on a 4.0 kg box with forces applied in opposite directions (15N WEST and 42N EAST) is 27N toward the EAST.
Step-by-step explanation:
The net force on a 4.0 kg box with a force of 15N toward the WEST and another force of 42N toward the EAST can be calculated by taking the difference between the two forces since they are in opposite directions.
The larger force (42N EAST) minus the smaller force (15N WEST) equals the net force acting on the box in the direction of the larger force. Therefore, the net force is 42N - 15N, which equals 27N toward the EAST.