A 10 kilogram box is being pushed across the floor at a constant speed of 2.0 milliseconds. If the coefficient of friction is 0.25, what force must be used to push it?

.. at a speed of 2.0 miilseconds."

"2 milliseconds" is not a speed. But that's OK, because the speed doesn't matter as long as it's a constant. If the speed is constant then the acceleration of the box is zero. So now from \sum F = ma you know that the sum of forces acting on the box is zero, so the force being applied to push it must exactly equal the opposing force of friction. Do you know how to calculate that?