Is it possible for a moving object to have a constant velocity and a changing speed?

The velocity of an object moving in a straight line path is given as a function of time by $v = 6t - 3t^2$,where $v$ is in $m/s$ and $t$ is in $s$. The average velocity of the object between $t = 0$ and $t = 2 \ s$ is

$A$ bus travels the first one-third distance at a speed of $10\; km/h$,the next one-third at $20\; km/h$,and the last one-third at $60\; km/h$. The average speed of the bus is ........ $km/h$.

$A$ car moves from $X$ to $Y$ with a uniform speed $v_1$ and returns from $Y$ to $X$ with a uniform speed $v_2$. The average speed for this round trip is

Write the relation between speed and the magnitude of velocity.

$A$ car travels a distance of $x$ with speed $v_1$ and then the same distance $x$ with speed $v_2$ in the same direction. The average speed of the car is