We can draw in a Venn Diagram with 3 circles. We first label the circles blueberries, raspberries, and blackberries. In the middle where all the circles intersect it, we write the number 10. Then, we label everything else.
All fruits - 10
Blueberries and raspberries - 15
Raspberries and blackberries - 2
Blackberries and blueberries - 18
Just blueberries - 16
Just raspberries - none
Just blackberries - 34
Adding these all up we get 95. Subtracting that from 100 we get that 5 people had no fruit at all.
(P.S. They should have had fruit. Fruit is good for you!)