CREATE TABLE table_35931 ("Year" CLOB, "Model" CLOB, "Length" CLOB, "Width" CLOB, "Fleet Number" CLOB)

What is the length of fleet number 501-506?
SELECT "Length" FROM table_35931 WHERE "Fleet Number" = '501-506'
SELECT "Length" FROM "table_35931" WHERE "Fleet Number" = '501-506'