Write out the answer. 这是一道应用题，请列式解答，并写出答语。
       Three cats are hungry. The yellow cat wants to eat twenty-one little fish. The white cat wants to eat twenty
little fish. The black cat wants to eat thirty-one little fish. How much fish do they want to eat?
1. 列式解答：                                    
2. 写出答语：                                    

参考答案：
1. 21+20+31=72
2. They want to eat seventy fish.

Write out the answer. 这是一道应用题，请列式解答，并写出答语。
       Three cats are hungry. The yellow cat wants to eat twenty-one little fish. The white cat wants to eat twenty
little fish. The black cat wants to eat thirty-one little fish. How much fish do they want to eat?
1. 列式解答：                                    
2. 写出答语：                                    

参考答案：
1. 21+20+31=72
2. They want to eat seventy fish.