Crate is being pushed a constant velocity. What forces are being used?

Since the crate is moving at constant velocity the net force on the crate is zero. Since the crate is moving we are referring to the coefficient of dynamic friction. R is the reaction and is equal to the weight of the block mg. The effort is now doubled so the forces on the block are not balance

Alinear relationship would look like a straight line on the graph. it could have a positive negative or 0 slope. so it could be a line potentially going in any direction but it must be perfectly straight.