When two balls are rolled in opposite directions at a speed of 10 km/hr inside a airtight container running at 100 km/hr speed which ball will reach the other end first?

All velocities are relative - is the 10 KPH speed of the balls measured relative to the container, or to the ground?

Imagine yourself on an airplane trying this experiment by rolling balls up or down the aisle - how would they behave, and what do you think the answer would be?