*I really don't know how to get started. I have done lots of the homework, but this one (and a couple of others) are really giving me PROBLEMS.*

Question

A stockroom worker pushes a box with a mass 10.5 kg on a horizontal surface with a constant speed of 3.00 m/s. The coeffecients of kinetic and static friction between the box and the surface are .330 and .400, respectively.

What horizontal force must the worker apply to maintain the motion of the box?
Answer expressed in N.

If the worker stops pushing, what will be the acceleration of the box?
Answer expressed in m/s^2.

I have difficulty with your opening statement, as this is some of the simplest force problems in existance. Perhaps you need to rexamine your efforts. Anyone can type a statement expressing what they think needs to be done.

Force friction= mass*g*coeffFriction

In the first case, to maintain the motion, the kinetic coefficent is used.
In the second case, the above force of friction is equal to mass*deaccaleration.