CREATE TABLE table_40300 ("Week" FLOAT, "Date" TEXT, "Opponent" TEXT, "Result" TEXT, "Attendance" FLOAT)

Mean attendance for December 22, 1980?
SELECT AVG("Attendance") FROM table_40300 WHERE "Date" = 'december 22, 1980'
SELECT AVG("Attendance") FROM "table_40300" WHERE "Date" = 'december 22, 1980'