CREATE TABLE table_78347 ("Name" CLOB, "Builder" CLOB, "Wheel arrangement" CLOB, "Works Number" FLOAT, "Built" FLOAT)

What is the average building year for Superb?
SELECT AVG("Built") FROM table_78347 WHERE "Name" = 'superb'
SELECT AVG("Built") FROM "table_78347" WHERE "Name" = 'superb'