CREATE TABLE table_11481 ("Year" FLOAT, "Chassis" TEXT, "Engine" TEXT, "Tyres" TEXT, "Points" FLOAT)

Tell me the average points with tyres of b and chassis of tf109
SELECT AVG("Points") FROM table_11481 WHERE "Tyres" = 'b' AND "Chassis" = 'tf109'
SELECT AVG("Points") FROM "table_11481" WHERE "Chassis" = 'tf109' AND "Tyres" = 'b'