They key to problems in which objects are being acted upon by a force at an angle with the horizontal is to realize that only the horizontal component of this force, i.e. the one parallel to the displacement, does the work.
Since no mention of friction is made, you can safely assume that the box has a frictionless motion. If you take
This means that work, which is done everytime a force acts through a distance, will be equal to
Plug in your values to get