Hi

I am afraid the answers are not correct

The usual way to manage this problem is to come back to the definition of the speed

And integrate on the 3 parts (for instance on the first part, v(t) is linear v(t) = at+b)

In your exercise you can do a little bit quicker due to the fact that the speed is linear with respect to time

On the first part it is equivalent to the average speed (70 km/h) during 10 minutes

On the third part it is equivalent to the average speed (70 km/h) during 5 minutes

Therefore the global is equivalent to

70 km/h during 15 minutes = 17.5km

20 km/h during 10 minutes = 3.33 km

The total distance is 20.83 km

The answers are right only if there is a typing error on the lowest speed : if you replace 20 km/h by 60 km/h then it is true