First of all ... there isn't a shred of information about direction here,
so you're in no position to talk about 'velocity'. That's not just a
big word for 'speed'. They're two different things. So let's just talk
about 'speed'.
Average speed =
(distance covered in some time)
divided by
(time to cover the distance).
You're given a distance and a time ? Great ! Divide the distance
by the time, and you have the average speed during that time.
And don't forget about the units.
(0.5 meter) in (1.5 seconds) ?
Average speed = (0.5 meter) / (1.5 seconds) = 1/3 meter/second .
.
.
etc.