At t $=10$ s$,$ a particle is moving from left to right with a speed of $5\mathrm{.}0$ m$/$s$.$ At t $=20$ s$,$ the particle is moving right to left with a speed of $8\mathrm{.}0$ m$/$s$.$ Assume the particle's acceleration is constant and that to the right is the positive direction. The acceleration, in m$/$s$^2$ was $-1\mathrm{.}3$ Determined its velocity at t$=0,$ in m$/$s$?$ Determined the time, in seconds, when its velocity is zero?