Answer:
See below
Step-by-step explanation:
Translating the weight of the box , mg, to the plane coordinates
Fdp = force downplane = mg sin 20.8
Fn = mg cos 20.8 so Ff = Force of friction = .0704 mg cos 20.8
SO the total force acting to slow the box is the sum of these two
= mg (.0704 cos20.8 + sin 20.8°) = 37(9.81) ( .4209) = 152.78 N
The initial KE of the box = 1/2 (37)(7.15)^2 = 945.77 J
Remember Force X distance = Work
the forces slowing the box must do this much work to stop it
152.78 * d = 945.77
d = 6.19 m