Final answer:
If you are standing on a scale in an elevator moving up with a constant speed, the scale will read your normal weight, which in this case is 120 lb.
Step-by-step explanation:
The question you've asked pertains to Physics, particularly concepts related to forces and motion. Specifically, it relates to how weight is perceived in different states of motion.
When standing on a scale in an elevator that is moving upward with a constant speed, there is no acceleration involved. This means that there are no additional forces acting on you aside from the normal force exerted by the scale, which is equal to your weight. Since the elevator is moving at a constant velocity (4 m/s in this case), there's no acceleration, so the only force acting on you is gravity, which is constant.
Therefore, if your weight is 120 lb when you are at rest, the scale will read 120 lb when the elevator moves upward at a constant speed. The correct answer to your question is (b) 120 lb.