Be quick about it -- tanks cannot take damage from weapons that use bullets. Look to your right to see a grenade launcher next to a box. Pick it up and stand behind the crates. Fire 40mm grenades on the tank. Its health is at the top. Try not to stand in the open when you fight it under the hard difficulty setting. It will take a lot of damage. You must be extremely fast to destroy it if you want to keep the gold medal. You will score at least 5,000 points if you manage to destroy it.