The teacher asked Wang Liang, Li Tao and Zhang Qing to do 200 questions. Each of the three got 120 questions right. And every question has been answered correctly, if the question that all three people answered correctly is called an easy question, and the question that only one person answered correctly is called a difficult question, then how many more difficult questions are there than the simple questions.
老师出了200道题让王亮、李涛和张清三人做．三人每人都做对了120道．且每道题都有人做对，如果把三人都做对的题称为简单题，只有一人做对的称为难题，那么，难题比简单题多多少道．
<gadget id="calculator">200 - 160</gadget>
<output>40</output>

<result>40</result>