CREATE TABLE table_29792 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code ( s ) " FLOAT, "U.S. viewers  ( millions ) " TEXT)

how many millions of north american viewers had the episode whose director was Michael Lembeck?
SELECT "U.S. viewers (millions)" FROM table_29792 WHERE "Directed by" = 'Michael Lembeck'
SELECT "U.S. viewers (millions)" FROM "table_29792" WHERE "Directed by" = 'Michael Lembeck'