Simplify the following text for a Grade 9 native English-speaking person.
Original: Boulogne-Billancourt is a sub-prefecture of the Hauts-de-Seine department and the seat of the Arrondissement of Boulogne-Billancourt .
Simplified: Boulogne-Billancourt is a sub-prefecture of the Hauts-de-Seine dÃ partement ans is in the Ã le-de-France region .