CREATE TABLE table_73269 ("Gas name" TEXT, "Chemical formula" TEXT, "Lifetime  ( years ) " TEXT, "20-yr" TEXT, "100-yr" TEXT, "500-yr" TEXT)

What is the 20 year for Sulfur Hexafluoride?
SELECT "20-yr" FROM table_73269 WHERE "Gas name" = 'Sulfur hexafluoride'
SELECT "20-yr" FROM "table_73269" WHERE "Gas name" = 'Sulfur hexafluoride'