Work = (force) x (distance)
= (100 N) x (5 m) = 500 joules .
Power = (work) / (time)
= (500 joules) / (15 sec)
= 33-1/3 joule/second = 33-1/3 watts .
Note:
I have assumed that the force was applied in
the same exact direction that the object moved.
If the force was applied at any angle to the
motion, then the work and the power are less.