Answer
See the detailed answer below.
Work Step by Step
a) See the figures below, and recall that: $F_n\rightarrow$ Normal force. $F_G\rightarrow$ Gravitational force (the weight of the object). $f_k\rightarrow$ Kinetic friction force. $T\rightarrow$ Tension force.
b) The acceleration here is directed down the inclined surface in the direction of the chosen negative $x$-direction since the net force is in the negative $x$-direction.
c) The direction of the speed is also down the inclined in the negative $x$-direction.
d) A box is pulled down a ramp by an unstretchable rope. The ramp is rough and since the box is moving down the ramp, the kinetic friction force acts up the ramp, as you see in the figures below.
