When the block will be moving up the incline, the external force will be up the incline and will be balancing the down the incline component of gravity.
When the block will be moving down the incline, the external force will be again up the incline and will be balancing the down the incline component of gravity. But in this case the external force will be on the back side of the block.
F=mgsin(θ)=2N





