Container $$A$$ contained $$\rm 350 mL$$ more water than Container $$B$$. After $$\rm 500 mL$$ of water was spilled out of Container $$A$$. Container $$B$$ had twice as much water as Container $$A$$. How much water was in Container $$A$$ at first? 
Overseas Competition->Knowledge Point->Word Problem Modules->Inverse Operation Problems->Inverse Operation Problems with Single Variable