A worker pulls horizontally on a crate across a rough horizontal surface, causing it to move forward with constant velocity. Force A is the force exerted by the worker and force B is the force of friction due to the surface. What is the relationship between A and B?

A > B

A = B

A< B

It will not slow down, but continue moving at constant velocity.

If an object is moving at a constant velocity (That means a constant speed in a straight line.) the net force acting on the object is zero, nothing. Why? It's motion is described by Newton's first law: An object at rest will remain at rest and an object in motion will remain in motion moving at constant velocity unless acted by an outside force.