question related to quadratic equation!
Let the number of children be x.
So each child has to give (x-1) gifts.
Thus, total number of gifts = x(x-1) = 132
x2 - x - 132 = 0
(x - 12) (x+11) = 0
x = 12 or x = -11
But, x cannot be negative.
Thus, the number of children is 12.
We hope that clarifies your query.