While time $t\geq 0$ a particle moves along a straight line. Its position at time $t$ is given by $$s(t)= 2t^3 - 21 t^2 + 36 t, \quad t \geq 0$$ where $s$ is measured in feet and $t$ in seconds.

(A) Use interval notation to indicate the time interval or union of time intervals when the particle is moving forward and backward.
Forward:
Backward:

(B) Use interval notation to indicate the time interval(s) when the particle is speeding up and slowing down.
Speeding up:
Slowing down:

("Speeding up" and "slowing down" refer to changes in speed, the absolute value of velocity.)