Simplify the following text for a Grade 6 native English-speaking person.
Original: Traveling an average of 22 mph , Couch used plastic bags filled with 75 litres ( 20 gallons ) of water as ballast against the 105 large helium balloons tied to his lawn chair .
Simplified: He tied 105 large helium balloons to his lawn chair . Couch used plastic bags filled with 75 liters water as weight to balance the balloons .