2 multiple choice questions.

For the first one, the box is moving with constant velocity, meaning the sum of the forces in a given direction will be equal to zero, as friction opposes motion, the frictional force is the horizontal component of the two tensions added together.
For the second, work done is equal to the force multiplied by the distance moved in the direction of the force, meaning that only the horizontal component of the tension is doing any work on the box.
Hope this helps