CREATE TABLE table_46497 ("Railway" TEXT, "Builder" TEXT, "Built" FLOAT, "Wheels" TEXT, "Location" TEXT, "ObjectNumber" TEXT)

Which Built has a Builder of brel crewe?
SELECT AVG("Built") FROM table_46497 WHERE "Builder" = 'brel crewe'
SELECT AVG("Built") FROM "table_46497" WHERE "Builder" = 'brel crewe'