Cup and liter both are measuring units.
A balloon is filled with a volume of 21.55 cups
Volume of balloon in liter L = ?
When we convert the measurement of cup into liter,
1 US customary cup = 0.236588 L
21.55 cups = 0.236588 x 21.55 = 5.0984765
So the volume of balloon in liter = 5.0984765 Liter