A crate with a mass of 40 kg is pulled by a force horizontally with constant speed for 10 m The kinetic friction force is 10 N What is the work done by the force?

If the speed is constant, then the forces on the crate are balanced, i.e. they add up to zero.

Since the kinetic friction force is 10N, then the puller must be pulling the crate with an equal force of 10N.

If he continues pulling with the force of 10N through a distance of 10 m, then the work he does is

(10 x 10) = 100 newton-meters or 100 joules.

The mass of the crate is utterly irrelevant to the discussion.