CREATE TABLE table_55822 ("Class" TEXT, "Operator" TEXT, "Number" FLOAT, "Year Built" TEXT, "Cars per Set" FLOAT, "Unit Numbers." TEXT)

What year was the class 253 larger than 18 built?
SELECT "Year Built" FROM table_55822 WHERE "Class" = 'class 253' AND "Number" > '18'
SELECT "Year Built" FROM "table_55822" WHERE "Class" = 'class 253' AND "Number" > '18'