CREATE TABLE table_15840 ("Year" FLOAT, "Entrant" TEXT, "Chassis" TEXT, "Engine" TEXT, "Points" TEXT)

What year did Elf Team Tyrrell have 39 points and a Tyrrell 007 Chassis?
SELECT SUM("Year") FROM table_15840 WHERE "Entrant" = 'elf team tyrrell' AND "Points" = '39' AND "Chassis" = 'tyrrell 007'
SELECT SUM("Year") FROM "table_15840" WHERE "Chassis" = 'tyrrell 007' AND "Entrant" = 'elf team tyrrell' AND "Points" = '39'