How many people learned of the sale from newspapers or the Internet but not from both? A

Question:

How many people learned of the sale from newspapers or the Internet but not from both?
A merchant surveyed 400 people to determine from what source they found out about an upcoming sale. The results of the survey follow:
180 from the Internet
190 from television
190 from newspapers
80 from the Internet and television
90 from the Internet and newspapers
50 from television and newspapers
30 from all three sources.