Our country is a country with poor water resources. The third grade students carried out water conservation activities. The students in class 31 saved 12.8 tons of water a week, which was 2.4 tons more than the students in class 2. How many tons of water did the two classes save in total?
我国是一个水源贫乏的国家，三年级同学开展了节约用水的活动，三1班同学一周节约用水12.8吨，比三2班同学多节约了2.4吨，两个班同学一周共节约用水多少吨？
<result>423.2</result>