Read this and answer the question. If the question is unanswerable, say "unanswerable".

The Roman Catholic Diocese of Charleston Office of Education also operates out of the city and oversees several K-8 parochial schools, such as Blessed Sacrament School, Christ Our King School, Charleston Catholic School, Nativity School, and Divine Redeemer School, all of which are "feeder" schools into Bishop England High School, a diocesan high school within the city. Bishop England, Porter-Gaud School, and Ashley Hall are the city's oldest and most prominent private schools, and are a significant part of Charleston history, dating back some 150 years.

Some of the oldest public schools in Charleston date back how long?
unanswerable