Simplify the following text for a Grade 7 native English-speaking person.
Original: Marzahn-Hellersdorf is the tenth borough of Berlin , formed in 2001 by merging the former boroughs of Marzahn and Hellersdorf .
Simplified: Marzahn-Hellersdorf is one of the 12 new boroughs of Berlin . It was created in 2001 when the old boroughs of Marzahn and Hellersdorf were merged ( joined together ) .