From the condition, one can say that the whole population is 33 people.
Then we have 33 people, of which 11 like mango, 22 like orange and 12 like none of them.
So in math, we can say that 33-12 = 21 like at least one of the fruits.
Then the number of those who like both the fruits is computed by: 11 + 22 - 21 = 12.