CREATE TABLE table_71158 ("Margin" FLOAT, "Score" TEXT, "Opponent" TEXT, "Venue" TEXT, "Year" FLOAT)

Name the sum of year for penrith panthers opponent
SELECT SUM("Year") FROM table_71158 WHERE "Opponent" = 'penrith panthers'
SELECT SUM("Year") FROM "table_71158" WHERE "Opponent" = 'penrith panthers'