CREATE TABLE table_40878 ("Week" FLOAT, "Date" TEXT, "Opponent" TEXT, "Result" TEXT, "Attendance" TEXT)

How many Weeks have a Result of w 17 13?
SELECT AVG("Week") FROM table_40878 WHERE "Result" = 'w 17–13'
SELECT AVG("Week") FROM "table_40878" WHERE "Result" = 'w 17–13'