Since Manuel is exerting a force of 10 N to the right, and Lynn is exerting a force of 15 N to the left, it means that Lynn is exerting a force of 5 N more than Manuel, meaning that the desk will move to the left, the direction Lynn is pushing it too.
Select a point on a distance-time curve graph. Draw a tangent to the curve at that point. Tangent -> hypotenuse of right angled triangle. Opp/adjacent in graph units is vel at that point -> in distance and/or time