Simplify the following text for a Grade 6 native English-speaking person.
Original: Peter Grimes is an opera by Benjamin Britten , with a libretto adapted by Montagu Slater from the Peter Grimes section of George Crabbe 's poem The Borough .
Simplified: The conductor Sergei Koussevitzky asked Britten to write an opera based on a poem by George Crabbe . The poem , called â The Boroughâ , was about the story of Peter Grimes .