Sudhin cycled at 8.5 km/h for 4 hours, then took an auto and travelled at 20 km/h for 1.5 hours, and then walked at 4 km/h for y hours. If Sudhin's overall average speed for the entire journey was 10 km/h, what is the value of y?
1
2
2
1.25
3
1.5
4
1.75