Velocity

Average velocity is the displacement divided by the time:

$$v = \frac{\Delta x}{\Delta t}$$

Its sign gives the direction. Speed is its size, without the sign.

On an x-t graph the velocity is the slope. A flat line means at rest; a line sloping down means a negative velocity.

The slope is $\Delta x$ / $\Delta t$ = $30\ \mathrm{m}$ / $5\ \mathrm{s}$ = $6\ \mathrm{m/s}$.