CREATE TABLE table_57986 ("Number Range" TEXT, "Builder" TEXT, "Introduced" FLOAT, "No. Built" FLOAT, "Region" TEXT, "Withdrawn" FLOAT)

when was the building withdrawn when the builder was ac cars and was introduced before 1958?
SELECT SUM("Withdrawn") FROM table_57986 WHERE "Builder" = 'ac cars' AND "Introduced" < '1958'
SELECT SUM("Withdrawn") FROM "table_57986" WHERE "Builder" = 'ac cars' AND "Introduced" < '1958'