本月JJ Math 26

26.

In a class of 120 students, 80 can speak English, 70 can speak Spain, 60 can speak French. If every student in the class can speak at least one of the languages, at least how many of students in class can speak all the three languages?

這題我的答案是30, 但看到有牛人說是0, 我看了解釋後還是不懂, 請問有人能夠解釋一下嗎?

感謝!!

最好把解释也写出来