Answer
100 N.
Work Step by Step
Assuming that you are pushing horizontally so that the crate's weight is canceled out by the floor's upward, vertical support force, the force of friction is 100 N.
The crate is in dynamic equilibrium so the net force on it is zero. Your push of 100 N (say, to the right) is canceled out by the frictional force of 100 N, directed to the left.
