Answer:
4 students
Step-by-step explanation:
As shown in the diagram, let U=[The total number of students questioned]

A=[Those who liked peanut butter ]

B=[Those who liked jam ]

x = those who like both peanut butter and jam.
Also 6 liked neither peanut butter nor jam.
From the diagram we can write the mathematical equation as follow and solve for x


We add x and subtract 30 to both sides.


Therefore 4 students like both peanut butter and jam.