CREATE TABLE table_7647 ("Week" FLOAT, "Date" TEXT, "Opponent" TEXT, "Game Site" TEXT, "Final Score" TEXT, "Record" TEXT, "Attendance" TEXT)

What is the Attendance with a Week that is 18?
SELECT "Attendance" FROM table_7647 WHERE "Week" = '18'
SELECT "Attendance" FROM "table_7647" WHERE "Week" = '18'