I need help with my math homework?

Belinda witch brewed 5 cauldrons of vampire soup and 1 cauldron of rat soup. the cauldrons held 15liters ,19liters,20liters,16liters,31liters and 18liters.she sold some of the cauldrons to wicked Wendy and some to nasty Natalie. Natalie purchase twice as many as Wendy . she kept the rat stew for herself. which ones did Wendy buy? which ones did Natalie buy?which one did she keep for herself? explain how you got your answer.