1. Mix sugar and 3 cups water in a pan and bring to a boil over medium-low heat, stirring until sugar dissolves. Turn off heat; stir in lemon slices and mint. Allow to cool, then strain.
2. Bring 4 cups of water to a boil. Place tea bags in a bowl; pour water over and let steep for 10 minutes. Remove and discard bags. Let tea cool.
3. In another bowl, mix lemon juice with 3 cups water.
4, Combine syrup, tea and lemon mixture. Cover and chill for at least 4 hours. Serve over ice, garnished with additional lemon slices and mint sprigs, if desired.