Read this: A cappella has been used as the sole orchestration for original works of musical theater that have had commercial runs Off-Broadway (theaters in New York City with 99 to 500 seats) only four times. The first was Avenue X which opened on 28 January 1994 and ran for 77 performances. It was produced by Playwrights Horizons with book by John Jiler, music and lyrics by Ray Leslee. The musical style of the show's score was primarily Doo-Wop as the plot revolved around Doo-Wop group singers of the 1960s.

How many works of a cappella in musical theater have been successful in Off-Broadway productions?
What is the answer? (If it cannot be answered, return "unanswerable")
four