The correct answer is 25 N.
A box is pulled to the right and the forces are as shown in the free-body diagram. The applied force which pulls the body is 125 N and is shown on the right hand side of the box. The kinetic friction force has to be in the negative x direction. This is because friction is always in the direction opposite to the motion. The only force in the direction of the negative x-axis is 25 N.
The correct answer is 25 N