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

$A$ 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

Five particles have speeds $1, 2, 3, 4, 5 \, m/s$. The average velocity of the particles is (in $m/s$):

$A$ car moves from $A$ to $B$ with a speed of $30 \ km/h$ and from $B$ to $A$ with a speed of $20 \ km/h$. What is the average speed of the car (in $km/h$)?

The position of an object moving along the $X$-axis is given by $x = \alpha + \beta t^2$,where $\alpha$ and $\beta$ are constants with appropriate dimensions and $t$ is time in seconds. The average velocity between $t = 2 \ s$ and $t = 4 \ s$ is $12 \ m/s$. If $\alpha = 8 \ m$,then the value of $\beta$ is: (in $m/s^2$)