Physicssss help pleaseee?!!?

The problem is in the first step where you calculated the velocity. Since the dock worker is pushing on the block for 5 seconds straight, the velocity is always changing (it continues to increase as he pushes on it). So the value of 1.6 m/s is not the velocity that the block is moving after 5 seconds, that is the *average velocity* of the block over those 5 seconds. The velocity is increasing constantly, so the average must happen half way through the worker's push, or at 2.5 seconds. Just use 2.5 seconds instead of 5 seconds in your second step, and you should be good to go!