Answer:
0.5 hour
Step-by-step explanation:
Given
Speed of Dina = 10 km/h
Distance = 20 km
So the time Dina taken to complete the track is:

The time taken by Dina is 2 hours. As masha started with dina but she was 4 km of the path left to cycle,
her distance covered in 2 hours was:

So we know the time and distance:
Now,

We have to calculate the time that will be needed by MAsha to complete the track:
As we know the speed and remaining distance

Masha needs 0.5 hour to complete the track ..