CREATE TABLE table_27138 ("Round" FLOAT, "Circuit" TEXT, "Date" TEXT, "Class A Winner" TEXT, "Class B Winner" TEXT, "Class C Winner" TEXT, "Class D Winner" TEXT)

In which round did Roy Salvadori won Class D and Alan Hutcheson won Class B?
SELECT "Round" FROM table_27138 WHERE "Class D Winner" = 'Roy Salvadori' AND "Class B Winner" = 'Alan Hutcheson'
SELECT "Round" FROM "table_27138" WHERE "Class B Winner" = 'Alan Hutcheson' AND "Class D Winner" = 'Roy Salvadori'