CREATE TABLE table_71125 ("Year" FLOAT, "Entrant" TEXT, "Chassis" TEXT, "Engine" TEXT, "Tyres" TEXT, "Points" FLOAT)

How many years were g Tyres and Minardi m187 used?
SELECT AVG("Year") FROM table_71125 WHERE "Tyres" = 'g' AND "Chassis" = 'minardi m187'
SELECT AVG("Year") FROM "table_71125" WHERE "Chassis" = 'minardi m187' AND "Tyres" = 'g'