Determine that quantity by following these steps:
1). Search your class notes or your textbook to find the definition of "Work".
2). Find the definition: Work = (force) x (distance)
3). Identify the quantities in the problem you're showing us:
Force = 100 N
Distance through which the force acts = (from 2m to 6m) = 4 m
4). Substitute the quantities in the definition of Work that you found:
Work = (force) x (distance)
= (100 N) x (4 m)
= 400 N-m
= 400 Joules of Work.