CREATE TABLE table_5557 ("Number" FLOAT, "Builder" TEXT, "Type" TEXT, "Date" FLOAT, "Works number" FLOAT)

Which Date has a Builder of alco schenectady, and a Number larger than 835, and Works number of 56566?
SELECT AVG("Date") FROM table_5557 WHERE "Builder" = 'alco schenectady' AND "Number" > '835' AND "Works number" = '56566'
SELECT AVG("Date") FROM "table_5557" WHERE "Builder" = 'alco schenectady' AND "Number" > '835' AND "Works number" = '56566'