Answer:
6 km/h
Step-by-step explanation:
For the fist half we must have a distance travelled and the time that this distance was travelled in, we will call this d1, and t1. For the second half we must also have a distance and a time: d2 and t2.
If we say that the total distace was 'x'


Now, let's find t1 and t2.
for the fist half the horse was traveling at a velocity of 12 km/h, using

We have for t1:

And for t2, since the horse now is traveling at 4 km/h:

And finally we can find the average velocity, using the formula:

Thus, replacing the values we found:
