A child carries a 3N book at a constant velocity 4 meters across a horizontal floor. What is the net work done?

Note that 4 m (meters) has the units of distance, not velocity.

By definition,

Work = Force x Distance

Therefore if a 3 N book is carried over a distance of 4 m, the work done is

3 * 3 4 = 12 J

Answer: 12 J