A box of books weighing 319 N is shoved across the floor by a force of 485 N exerted downward at an angle of 35° below the horizontal. a) If uk between the box and the floor is 0.57, how long does it take to move the box 4.00 m, starting from rest? b) If uk between the box and the floor is 0.75, how long does it take to move the box 4.00 m, starting from rest?