Answer: The number of people who drank both is 90
This is because we need to subtract 350 people from 500 people, because we know that they didn't drink the drink. We have 150 people left. Another 60 people don't drink the drink at all, so we need to subtract that from the remaining 150 people left. We get the solution of 90 people who could only have drank both drinks based of of the givens you have provided.